The document discusses using C# for cloud and mobile applications. It covers using C# for cloud services on Azure, building C# clients for mobile platforms, and enabling communication between C# cloud services and clients. Several example applications are presented that demonstrate these concepts in practice, including apps for photo sharing, conferences, advertising, and more. The document argues that C# is a good choice due to shared code, performance, tools/libraries, and existing C# skills. It also outlines different architectural approaches from simple to sophisticated for clients and servers.