We owe Williamson for the formal introduction of hybrid organizations as essential building blocks in ‘the institutional structure of production’. The analysis of these institutional arrangements, which culminated in The Mechanisms of Governance, provided a unified approach to the variety of setting within which transactions are embedded, opening a new perspective on a cornerstone of modern economies. This essay explores the past, present, and future of this breakthrough. First, it reviews the progressive integration of hybrids as a category of their own in the classic ‘make-or-buy’ model, inserting hybrids as an ‘intermediate’ form different from markets in that adaptation cannot be done unilaterally and different from ‘unified organizations’ in that adaptation cannot be done by fiat. Second, it shows how this initial characterization of hybrids, besides providing a coherent approach to empirical research available at the time, gave a powerful impulse to new contributions, identifying more rigorously the fundamental features of hybrids, throwing light on why firms go hybrid, and explicating the governance structure chosen. Last, it offers insights on a research program that remains a work in progress, delineating new terrains to explore and new puzzles to solve.