We chose Go because it offers amazing facilities for introspecting its own source code, such as go/doc (http://golang.org/pkg/go/doc/ and https://sourcegraph.com/code.google.com/p/go/.GoPackage/go/d...) and go/types. So, it was the obvious choice to use to prototype Sourcegraph. The reputation of the core team and our initial experience learning it were also factors.