The Evergreen open-source library system serves library consortia composed of hundreds of branches with millions of patrons - for example, the Georgia Public Library Service PINES system. One of the claimed advantages of Evergreen over alternative integrated library systems is the underlying Open Service Request Framework (OpenSRF, pronounced "open surf") architecture. This article introduces OpenSRF, demonstrates how to build OpenSRF services through simple code examples, and explains the technical foundations on which OpenSRF is built.