Dominant architectural style for HTTP APIs. Critiqued in the talk for forcing clients into N+1 fetches (video, channel, each comment, each author, next video, next channel, …) and, in YouTube's case, for leaking server-side internals — the 'part' parameter, snippets vs contentDetails, and per-part quota costs — into every client. Motivates GraphQL, Falcor, and Pathom/EQL.