To fully exploit the business opportunity available through application programming interfaces (APIs), your designers must consider each API's purpose and audience as they select messaging types for your API's use and design the details of how you use each messaging type. The core design concerns boil down to balancing reach with other design goals. Simpler forms of REST will reach the broadest open Web API user audience, but SOAP and message queuing can lower the cost of achieving your design goals for B2B APIs and internal APIs. As part of a series on API design practices, this report examines industry data and directions for designing messaging styles using REST, SOAP, MOM, and other special API messaging styles.