We live in an era of service computing with cloud computing platforms, social computing, and mobile computing. One of the most significant characteristics of the era is that any device connects to any service and any service connects to any data with a cost-effective way. The connection between device and service as well as between service and data is built by modern Web APIs. The shift is not only for using software in particular business, but also for engaging other business and people – internal developers, partners, customers, and the world at large, through exposing software interfaces by APIs. The trend is creating a new business reality – API Economy. It is leading an evolution of the traditional SOA paradigm to cloud-enabled, social-enabled, and mobile-enabled modern lightweight SOA. There is increasing automation of processes, transactions, and distribution across many industry sectors and organizations. This paper describes the API Economy and the emergence of API management, its building blocks, its role in service infrastructure. Moreover, API-central architecture patterns, its reference architecture, and its deployment topologies can be found in a newly coming book Service Infrastructure.