What is a demand-side platform? An in-depth guide for beginners

TL;DR: What is a DSP?

• A demand-side platform (DSP) is automated software that helps advertisers buy, manage, and optimize digital ads in real time across websites, apps, and channels.
• DSPs connect to ad exchanges and supply-side platforms (SSPs) to execute programmatic advertising through audience targeting and automated campaign optimization.
• Leading DSPs like StackAdapt are evolving beyond traditional media buying, using AI, 1st-party data, and owned channels to orchestrate campaigns across the full customer journey.

The consumer journey is increasingly fragmented and only getting more complex.

Although there’s no industry-wide consensus on how many touchpoints it takes to convert a customer, today’s consumers typically encounter brand messages across multiple channels—scrolling through apps, streaming TV, and passing by ads in the real world—multiple times before completing a purchase.

As a result, marketers continue to move away from the siloed, single-channel campaigns that once defined digital advertising and toward more connected, multi-channel strategies.

To do that, they’re turning to demand-side platforms (DSPs), which allow advertisers to purchase and manage digital ad inventory across multiple channels and media partners with more flexibility, precision, and control.

Because of this, programmatic advertising is quickly becoming the default way advertisers buy digital media: Not only is programmatic’s share of display advertising spending expected to account for nearly 93% of total US digital display ad spending by 2027, but even traditionally direct-buy channels like digital out-of-home (DOOH) are moving in the same direction, with over a third of DOOH ad spending projected to be transacted programmatically by then.

But what exactly is a DSP, and how do marketers use one to plan, activate, and measure programmatic campaigns across channels?

Understanding how DSPs work—and how they’re evolving—is key to successfully navigating today’s programmatic landscape.

Here’s what marketers need to know.

What is a demand-side platform?

A DSP is software that lets advertisers automate the buying, placement, optimization, and measurement of digital ads in real time across multiple websites, apps, and platforms.

DSPs simplify the sometimes complex process of programmatic advertising by allowing marketers to set budgets, define audiences, upload creatives, and manage multiple campaigns simultaneously, all from a single platform.

What is the difference between a demand side-platform vs. a supply-side platform?

To understand how programmatic advertising works and what role a DSP plays in the process, it helps to look at the programmatic ecosystem through a buyer-and-seller lens.

• A DSP sits on the advertiser side of the equation. It’s used by brands and agencies to buy ad space, with a focus on reaching the right audiences and optimizing spend against specific marketing goals.
• A supply-side platform (SSP) sits on the publisher side. It’s used by media owners, such as websites, apps, and screen networks, to sell their available ad space—all with the goal of maximizing revenue from each impression.

Ad exchanges sit between DSPs and SSPs, acting as the go-between marketplace where impressions are bought and sold, often through real-time bidding (RTB). Through these exchanges, SSPs make inventory available to multiple DSPs at once, giving advertisers access to a broad range of placements without needing to negotiate with individual publishers directly.

When an opportunity becomes available, SSPs offer it into the exchange, DSPs bid based on the advertiser’s pre-determined criteria, and the winning ad is served.

The whole process takes less than a millisecond, faster than a page can fully load—making a DSP the perfect partner for purchasing multiple ad placements at scale without sacrificing control.

Here’s a brief side-by-side comparison of the differences between a DSP vs. SSP:

Although traditional DSPs focus on buying and optimizing paid media, platforms like StackAdapt are expanding beyond that: bringing together programmatic channels like connected TV (CTV), native, display, and audio with owned channels like email—powered by 1st-party data and real-time signals—to create more orchestrated customer journeys.

Types of programmatic ad targeting

Using a DSP, advertisers can define who they want to reach, where, and under what conditions, then rely on automation to deliver ads to the right audiences—whether they’re browsing the web at work, playing a game on their smartphone, or streaming content from the comfort of their home.

These targeting capabilities include audience targeting, as well as contextual and device-based targeting—giving marketers flexibility over both who sees their ads and where they appear.

Here are some of the most common types of programmatic ad targeting:

• Demographic targeting reaches audiences based on attributes like age, gender, or income brackets (where available).
• Geographic targeting allows advertisers to control where ads appear, from country and region down to city or zip/postal code, making it easier to support everything from national launches to hyper-local campaigns.
• Behavioral targeting focuses on past browsing activity and engagement signals, helping brands connect with users who’ve already shown interest in certain products or services based on their online behavior.
• Interest-based targeting reaches audiences based on inferred interests or affinities—such as fitness or travel—helping brands connect with consumers around what they care about.
• Contextual targeting places ads alongside relevant content, ensuring creative and messaging align with the page, app, or environment where the ad appears.
• Device targeting tailors delivery based on device type—such as mobile, desktop, tablet, or CTV device (like a smart TV or external device)—as well as operating system or browser, depending on campaign goals.
• Retargeting re-engages users who’ve previously visited a website, used an app, or taken a specific action, helping reinforce messaging and guide them further along the customer journey.

When done intentionally, the right combination of targeting tactics can help make campaigns more relevant, efficient, and cost-effective.

Types of programmatic media buying

When buying inventory through programmatic advertising, advertisers use DSPs to choose between two broad approaches: auction-based buying and programmatic direct deals. Each offers a different balance of scale, control, and predictability, depending on campaign goals.

Programmatic auctions

Programmatic auctions use RTB to buy inventory through auctions facilitated by ad exchanges. Pricing in these environments is dynamic, changing in real time based on demand, competition, and the value of each impression. This approach prioritizes scale and flexibility, allowing advertisers to evaluate and bid on impressions through a DSP as they become available, and typically takes place across one of two environments:

Open exchanges

The open exchange offers the largest scale, giving advertisers access to inventory from a wide range of publishers with minimal barriers to entry. This approach provides both broad scalability and the opportunity to reach new, highly relevant audiences across a wide range of publishers, streamers, and in-app environments.

Private marketplaces (PMPs)

PMPs are invitation-only auctions where a limited group of advertisers can bid on a publisher’s inventory. Because access is restricted, PMPs often feature more selective placements and provide advertisers with greater control over where their ads appear. This makes PMPs a common choice for brands seeking a balance between automation and publisher-curated inventory that may not be available through the open exchange.

As a result, PMP deals, at least for US digital display ad spending, are expected to grow at a CAGR of 16.7% over the next two years and account for nearly three-quarters of programmatic display ad spending by 2027.

Programmatic direct deals

Unlike programmatic auctions, programmatic direct deals remove the auction from the equation, allowing advertisers to agree on pricing and terms in advance while still using programmatic advertising technology to execute, deliver, and measure campaigns.

There are two primary types of programmatic direct deals advertisers use:

Programmatic guaranteed

Programmatic guaranteed deals closely resemble traditional direct buys, but with campaign management, delivery, and reporting handled through a DSP rather than manual insertion orders (IOs). Advertisers and publishers negotiate a fixed price and a guaranteed number of impressions, with delivery committed in advance. These deals provide predictable reach and access to premium inventory, making them well-suited for campaigns that require more certainty around ad placement and how many people each ad will reach.

Preferred deals

Preferred deals (also known as programmatic non-guaranteed) also involve pre-negotiated pricing, but without a delivery guarantee. Advertisers receive priority access to a publisher’s inventory at a fixed rate and can choose whether to buy each available impression. If they pass on the opportunity, the inventory is made available through PMPs or open auctions.

How this differs from traditional direct buys

Before programmatic advertising, inventory was typically purchased through traditional IOs, which required manual negotiation, fixed commitments, and provided limited flexibility once campaigns were live. While IOs can still be useful in certain situations, they often lack the speed, transparency, and optimization capabilities that programmatic buying enables.

Programmatic deals—whether auction-based or direct—combine automation with control, allowing advertisers to choose the buying approach that best fits their goals without sacrificing efficiency.

Types of demand-side platform service models

Not all DSPs are used the same way. While the underlying technology is similar, most platforms offer different service models—typically self-serve, managed, or, most commonly, a combination of both.

In practice, the difference isn’t the platform itself, but who’s running the campaigns and how involved your team wants to be in day-to-day execution.

Self-serve DSPs

With a self-serve DSP, advertisers or agencies manage campaigns directly in the platform themselves. That means setting up audience targeting, launching campaigns, adjusting budgets, testing creative, and optimizing performance on their own.

Self-serve DSPs offer the most control, speed, and flexibility, making it a strong fit for in-house teams and agencies with advanced programmatic expertise that want to iterate on campaigns quickly and monitor day-to-day performance more closely.

Full-service DSPs

In a full-service or managed DSP model, campaigns are run by a dedicated team or partner on the advertiser’s behalf. The team handles aspects of planning, activation, optimization, and reporting on behalf of the client, allowing advertisers to stay more hands-off and focus instead on broader strategic planning.

This approach can be helpful for teams that lack in-house traders with media buying expertise or teams that need additional support navigating programmatic buying.

Both models can be effective. The right choice depends on your resources and how involved you want to be.

Here’s a quick comparison chart explaining the core differences between self-serve and managed DSP service models:

StackAdapt offers both self-serve and managed services: teams can run campaigns independently through our intuitive platform, or partner with StackAdapt experts, who provide more strategic support, creative guidance, and help make ongoing optimizations—improving performance and ROI while reducing operational complexity. Learn more about our client services.

How do demand-side platforms work?

To understand how programmatic advertising and DSPs work, let’s look at a simple example you’ve probably experienced countless times: seeing a display ad while browsing a website.

Here’s a step-by-step breakdown of the whole process:

Step 1: Campaign setup

Let’s say an advertiser wants to promote a new product or service using a DSP. First, they choose a specific goal for their campaign—such as improving brand awareness, driving demo sign-ups, or increasing sales—and use the DSP to create and manage the ad campaign, setting the targeting criteria and budget.

Step 2: Initial user interaction

The process starts when a user visits a website—like a news site or blog—with available ad space. The website’s SSP identifies the opportunity and notifies an ad exchange that an impression is available for auction.

Step 3: The auction begins

The ad exchange acts as a digital marketplace, sending bid requests to DSPs like StackAdapt. This request includes pseudonymized details about the user and information about the ad space, such as the type of content on the page and the size of the ad.

Step 4: The bidding process begins

The DSP uses machine learning to evaluate whether the impression aligns with the campaign’s targeting criteria and performance goals. It then decides whether it’s worth bidding on. It considers factors like the advertiser’s target audience, budget, and campaign goals to determine how much to bid, or whether to bid at all.

Step 5: A bid is selected

The ad exchange then collects bids from all the DSPs with eligible campaigns and determines the highest bidder in real time. The winning DSP is notified, and the ad creative gets displayed to the user on the publisher’s website. The selected ad is instantly displayed to the user on the website, all within a fraction of a second.

Step 6: Campaign optimization

After the ad gets served, marketers can track programmatic KPIs and metrics to understand the impact of their campaigns. They can then use this data to adjust targeting, budget allocations, channel selection, and creative elements—like messaging or imagery—to improve the performance of future campaigns.

Still confused? Here’s a simplified visualization of how DSPs work:

Although the process may differ slightly for other channels like CTV, DOOH, or programmatic video, much of it remains the same—namely, the use of automation and real-time decision-making to evaluate each opportunity and place ads where they’ll drive the strongest performance.

What are the benefits of using a demand-side platform?

DSPs give marketers a more efficient, flexible way to plan, activate, optimize, and centralize digital marketing campaigns at scale without sacrificing control or performance.

Here are some of the key benefits of using a DSP:

Automated media buying

DSPs automate the previously time-consuming practice of purchasing digital ad inventory. Instead of working publisher by publisher, marketers can launch campaigns faster and manage media spend and pacing from a single platform.

Greater efficiency and less waste

Because DSPs buy impressions based on specific criteria, budgets go toward the opportunities that are most likely to reach their goals. This helps reduce wasted ad spend, streamlines campaign execution, and improves overall ROI.

More precise audience targeting

DSPs make it easier to reach specific audiences using a mix of 1st-party data, 3rd-party audience segments, and contextual signals. Marketers can target potential customers based on their behaviors, interests, locations, and other demographic attributes— like age or household income—to deliver ads that are more relevant to consumers as they move across different devices, platforms, and channels.

Broader inventory access

A DSP gives advertisers access to a wide variety of inventory across websites, apps, and streaming environments (whether that’s free ad-supported streamers like Tubi or live sports broadcasts like the Super Bowl or Olympics). This makes it easier to gain incremental reach, maintain brand consistency, and run campaigns across multiple channels, which is proven to be one of the most effective ways to improve performance across the funnel. For example, internal StackAdapt data shows that expert-tier advertisers who run multi-channel campaigns often see 47% higher click-through rates than single-channel campaigns.

Higher-quality media

Many DSPs and AI advertising platforms like StackAdapt provide access to premium publishers and curated inventory that traditional buying methods or smaller advertisers don’t always have access to. This gives advertisers the ability to show up in trusted, high-quality environments, like iHeartMedia podcasts, to improve brand perception and overall impact.

Centralized campaign management

DSPs bring campaign planning and execution into one place. Marketers can set budgets, upload creatives, define their target audiences, and manage campaigns across multiple channels at once, reducing operational silos and making day-to-day execution more efficient.

Real-time optimization

Because DSPs collect performance data as campaigns run, marketers can adjust bids, budgets, targeting, and delivery in real time. This makes it easier to improve results by tweaking campaigns while they’re in flight, rather than waiting until the end to learn what worked and (once it’s already too late) what didn’t.

Unified reporting and measurement

DSPs consolidate reporting across channels and placements, giving marketers clearer visibility into performance. With everything in one view, it’s easier to spot cross-channel performance trends, understand what’s driving results, and make more data-informed optimizations to improve campaign performance.

AI-powered optimization

DSPs use machine learning to support optimization, helping campaigns improve performance by automatically adjusting bids, budgets, and ad delivery in real time.

Turning cart abandoners into paying customers

Learn how Vallo Media increased CTR for Global Industrial by 60% using DCO in StackAdapt to re-engage customers.

What are the top-rated demand-side platforms?

Choosing the right DSP depends on a variety of factors and business priorities—from industry focus and feature depth to campaign optimization capabilities, integrations, reporting accuracy, and usability.

G2—the world’s largest B2B software review marketplace—has been collecting professional reviews and providing comparative insights based on real user feedback for well over a decade.

1. StackAdapt

StackAdapt has been consistently ranked #1 in G2’s best demand-side platform category. Based on G2’s current category rankings and verified user reviews at the time of writing, StackAdapt is also rated the easiest-to-use DSP by G2 reviewers. The platform is used by teams of all sizes, from enterprise advertisers to small and medium-sized businesses, with reviewers frequently highlighting its accessibility, intuitive interface, and flexibility.

Although its roots are in native advertising, StackAdapt is widely used by agencies and in-house teams for programmatic campaigns across channels including CTV, DOOH, display, audio, email, and, more recently, ChatGPT and direct mail.

One of StackAdapt’s most frequently cited strengths in G2’s analysis is its targeting functionality, with strong reviewer ratings for demographic and behavioral targeting, retargeting, geotargeting, and contextual targeting. These capabilities can help advertisers build more tailored campaigns, whether they’re reconnecting with past website visitors, running localized ads, or aligning creative with relevant environments.

2. Quantcast

Quantcast is recognized in G2’s analysis for AI-powered audience targeting, ease of use, and an accessible campaign management experience. Reviewers frequently highlight its straightforward setup, clean interface, and campaign dashboard, making it a practical option for teams looking to activate and monitor programmatic campaigns without a steep learning curve.

3. The Trade Desk

In G2’s analysis, The Trade Desk is recognized for omnichannel scale, data depth, premium inventory access, and precise audience targeting. G2 describes the platform as widely trusted by agencies and enterprise advertisers managing cross-channel campaigns across display, video, native, audio, and CTV. Reviewers frequently highlight its strong cross-device targeting capabilities, granular audience segmentation, and machine-learning-driven optimization tools, which can help advertisers manage complex campaigns across channels.

4. Viant

Viant Technology is recognized for audience targeting, CTV advertising, and advanced TV/CTV campaign management. G2 describes the platform as widely trusted by media teams and agencies running omnichannel campaigns where deterministic audience matching and household-level targeting are important.

5. Simpli.fi

Simpli.fi is recognized for hyper-local targeting, dynamic creative optimization, and hands-on customer support. G2 reviewers frequently highlight the platform’s ability to reach highly specific audiences, including ZIP-level and geo-fenced segments, which may make it a practical option for regional and localized campaigns.

Demand-side platform FAQs

Can you see clicks and sales in demand-side platforms?

DSPs can show clicks on your ads, including total clicks and click-through rate. DSPs can also track sales or other conversions when conversion tracking is set up, such as through a pixel, tracking tag, or server-to-server integration. These conversions may include purchases, form fills, sign-ups, or other actions that happen after someone clicks on or views an ad.

What are the top 5 DSPs?

The top five DSPs, according to G2’s analysis of verified user reviews, are StackAdapt, Quantcast, The Trade Desk, Viant, and Simpli.fi.

What is the best demand-side platform for small and small-to-medium-sized businesses?

StackAdapt is the top-rated DSP for small and mid-sized businesses, according to G2. Reviewers highlight its ease of use, flexible budget requirements, strong targeting capabilities, and hands-on customer support.