I am excited to announce The Forrester Wave™: Sell-Side Platforms, Q4 2024. This is the first Forrester Wave of the sell-side platform (SSP) provider category since 2014, and a great deal has changed in those 10 years.

In 2014, ad exchanges and SSPs converged, but mobile and video advertising remained siloed from display advertising — programmatic’s bread and butter. As the market matured, SSPs pushed closer to agencies and the buy side, seeking to cultivate unique, consistent advertiser demand and improve deal economics for publishers. At the same time, header bidding empowered publishers to access demand from multiple SSPs to increase fill rates with greater control. When the dust appeared to have finally settled, a tsunami of antitrust lawsuits broke in 2024, promising to permanently reshape the SSP landscape.

Today, publishers rely on SSPs to build addressable audiences, manage multiple deal types, and integrate a variety of third-party data sources — all in the service of filling every ad slot with the highest bid available from a trusted advertiser. Digital publishers now exist across more surfaces than ever, from the Las Vegas Sphere to the podcast in your ear. As a result, Forrester now defines an SSP as:

Technologies that empower digital publishers to sell, manage, and optimize advertising space across connected environments.

Given the importance and business impact of customer experience, we focused the evaluation on customers — specifically, which vendors help publishers deliver the cleanest, most user-friendly experience possible. This meant focusing on how the vendor connects publishers with relevant buyers while transacting less personally identifiable information and more anonymized tokens. Our evaluation revealed three significant differentiators among the vendors. Publishers should:

  1. Look for a vendor that plays well with others. SSP customers we interviewed consistently validated that interoperability, with flexible header bidding solutions for multiple environments, is key to SSP partnerships. A few vendors offer their own bid wrapper solution, potentially sacrificing their own revenue on some deals to provide publishers greater control and transparency.
  2. Short-list vendors that prioritize ad security. With more consumers blocking ads than ever before, and the technology to spoof and deepfake more accessible than ever, the long-term financial health of publishers and the safety of the open web are dependent on keeping bad actors in check.
  3. Expect more than “works with common identity solutions.” With data deprecation eroding the presence of third-party cookies across browsers and beginning to impact the presence of IP addresses and cookies, publishers need SSPs to provide alternative methods to maximize yield using zero- and first-party data connections, as well as provide clean room technologies to transact identifiers in a safe environment.

Our research also observes a shift in vendor dominance. While some stalwarts remain leaders in the space, others have ceded ground to smaller, or newer, rivals more closely attuned to publisher demands and responsive to industry trends.

To help you navigate the evolving SSP market, The Forrester Wave™: Sell-Side Platforms, Q4 2024, is now live. It identifies the 10 most significant SSP vendors — Adform, Amazon Ads, Equativ, Google, Index Exchange, InMobi, Magnite, Microsoft, OpenX, and PubMatic — and scores them on 33 criteria. Use this report to identify the SSP capabilities that matter most to you, including curating your inventory for agency and endemic buyers, leveraging new identity currencies to create seller-defined audiences, and more.