In the previous chapter, I observed how the notion of platforms has changed throughout recent decades from signifying a computational system (Bogost and Montfort, 2009) or a programmable architecture (Van Dijck et al, 2018) to a more general principle of organization (Kenney and Zysman, 2020; Stark and Pais, 2020) and a business model aimed at cornering markets and reaching monopoly status (Langley and Leyshon, 2017; Srnicek, 2017; Peck and Phillips, 2020). This can be related somewhat to the general transformation of platform companies and market orders during this time span, such as the change in the game industry from a market order dominated by a few console owners to one dominated by large tech companies from outside the gaming industry. While the platform as a computational system or programmable architecture is easily identified as the key principle of power in a market order controlled by console owners, the large tech companies control the market through their storefronts or extended market places (Doyle, 2013) and through their financial power to dominate the entire market field. One significant theme that runs through this course of development is the integration of retail into platform architectures, and the increasing focus on platforms as markets. Thus, another aspect of platforms which is often foregrounded is that they constitute multi-sided markets (Rochet and Tirole, 2003; Evans and Schmalensee, 2016; Van Dijck et al, 2018) that let different groups of customers meet on attractive terms. The aim of this chapter is to interrogate more systematically what this aspect of platforms involves. Are platforms primarily to be understood as multi-sided markets or do they integrate market components to various extents? Are all interactions taking place on platforms to be considered market interactions or is this classification reserved for specific types of interaction on platforms? And does the notion of multi-sided markets sufficiently address complex market constructions of platforms such as Steam?

In the subsequent sections, I will firstly take a closer look at the notion of multi-sided markets in platform studies. As an extension of this, I will describe and discuss how markets should be defined, as this concept is taken more or less for granted across disciplines.