The modern economy is built on interconnection. This manifests itself, in part, through network effects as traditionally conceived, whereby the value of a product increases with the number of users. These network effects can be thought of as demand-side externalities or demand-side economies of scale. But thinking of them in this way reminds us that similar – and equally interesting – effects can be seen on the supply side, in the vast number of complementary inputs that go into producing many products and services in today’s economy. And the two phenomena interact, because markets with powerful demand-side economies of scale tend to create ecosystems in which industry participants – including the producers of those complementary inputs – very much want to participate.