Digital platforms have reshaped many product markets and play an increasingly important role in economies around the globe. Some of these platforms have become powerful players and may possess a lot of market power. Economists use a number of indicators to assess market power. In this article we...

In many markets, user benefits depend on participation and usage decisions of other users giving rise to network effects. Intermediaries manage these network effects and thus act as platforms that bring users together. This paper reviews key findings from the literature on network effects and...

Lecture on the first SFB/TR 15 meeting, Gummersbach, July, 18 - 20, 2004: We develop a general theoretical framework of trade on a platform on which buyers and sellers interact. The platform may be owned by a single large, or many small independent or vertically integrated intermediaries. We...