Simulated markets are a fascinating paradox for Market Studies. They are markets organized around nothing. No real property rights get exchanged when markets are “only” simulated. They are unproductive in the sense that simulated markets produce no surplus for anyone. They are markets that do not actually exist. Yet, simulations of market processes play an increasingly important role in market practices as well as in wider business pedagogy. This chapter uses historical and contemporary evidence on the development and uses of market simulations in various settings – ranging from business schools to Wall Street – to test the post-performativity paradigm in Market Studies. The chapter shows that real-world market arrangements are changed not with the help of economic models, economic theories or economists themselves, but rather through business school teachers, family accountants, software tinkerers and designs that emerged completely outside the sphere of economic theory and modelling. By studying the early uses of electronic spreadsheets for market simulations, we can see that market arrangements require calculative communities rather than economists.