Over the past decade, public service media (PSM) have increasingly distributed content through digital platforms, most prominently YouTube, Facebook, Twitter, and Instagram. This article explores how this process of platformization, the integration of digital platforms in PSM, affects the public service remit of promoting key public values, such as universality, independence, and diversity. Specifically, it interrogates how Dutch PSM imagine platforms and their users, as well as how these imaginaries affect online public service strategies. The starting point is the notion of platform imaginaries : the ways in which social actors understand and organize their activities in relation to platform algorithms, interfaces, data infrastructures, moderation procedures, business models, user practices, and audiences. The analysis of these imaginaries builds on key public service policy documents and 15 interviews with employees from the NPO (Nederlandse Publieke Omroep; the governing body), the broadcasting associations, SKO (audience measurement service), and the Ministry of Education, Culture and Science. Our analysis of these materials shows that the online strategies of Dutch PSM are guided by three imaginations of platforms as (a) intermediaries that function on the basis of specific “laws,” (b) places where new audiences reside, and (c) powerful corporations that largely operate beyond the national sphere of influence. These platform imaginaries consist of a complex of interrelated observations, arguments, ideas, and practices, which are generally accepted and partly contested. The main bone of contention is how platform audiences should be seen. It has been difficult to reconcile competing ideas about audiences and, consequently, about the role of PSM in a platform environment, as broadcasters and policy makers lack the necessary (aggregate) data to determine how the media landscape is exactly changing and what the best public service response is. The conclusion of the article proposes a number of steps to resolve ...