What does an SEO agency do?
An SEO agency improves how your site ranks in Google and other search engines. That work spans three layers: technical SEO (site speed, crawlability, indexation, structured data), on-page SEO (title tags, content targeting, internal linking), and off-page SEO (backlink acquisition, digital PR, authority building). Most US SEO agencies also handle content strategy and production. The strong ones start by auditing what's already broken; the weak ones sell "more content" as the answer to every problem.
What the firms actually sell
Search engine optimization is the most frequently listed service in The Wall. 551 of the 1,738 listings that publish a service list name it. The company they keep tells you what the job has become: 294 of those 551 also list pay per click, 202 list web design, and 139 list content marketing.
That is the shape of the work rather than a marketing accident. Rankings move on technical fixes to the site, on pages somebody has to write, and on demand that paid search often uncovers first. 446 of the 551 firms run fewer than 50 people, so in practice a small team covers all of it.
How to use this
When a proposal arrives, split it into the three jobs and ask who does each one. If the answer to "who writes the pages" is your team, that is a content budget you have not counted yet. If the answer to "who ships the technical fixes" is your developer, that is a queue you do not control.
How this was computed. Every figure on this page is counted from The Wall's own directory of approved, US-headquartered, machine-verified-live listings: 3,460 of them in the snapshot captured 2026-09-14. Rates, minimum project sizes, team sizes, founding years and ratings are provider-declared figures published on public profiles. 1,738 of those listings publish a service list, and that field holds at most 4 services per firm, so service counts are counts of what firms name first rather than everything they sell. Percentages of disclosed values exclude listings that publish no figure. Nothing here is modeled or estimated. Sourcing standards: editorial policy.
Why this matters
Google puts this question in People Also Ask for the "seo agency" query, which means buyers are asking it while they shop. The Wall answers it from the directory position: we index 3,460 verified US growth-services vendors across 10 pillars, so the figures above come from those records rather than from a survey.
If you are evaluating vendors in this category, the SEO pillar page carries the full US firm list with rate, team size and headquarters filters.