Platforms and their ecosystems have become one of the most successful organisational forms in recent decades. Platforms sit between traditional (centralized) hierarchical firms and (decentralized) markets and contain elements of both. One of the core differences to traditional firms is that a significant part of the value created by platform ecosystems comes from actors outside the direct control of the platform owner itself - the complementors. This lecture will explore how the relationship between complementors and platforms has evolved and how research has settled on an established way of studying these relationships, and platform strategy more generally. Finally, the lecture will outline some recent developments and end with a call for research adapting to these recent developments.