This document proposes a framework for classifying social machines. It defines social machines as systems involving both algorithmic and social components that interact and evolve over time. The objectives are to identify constructs for describing and comparing social machines. A methodology elicited constructs from examples of social machines. The resulting classification framework clusters constructs around general description, purpose/tasks, participants/roles, motivation/incentives, and technology. Next steps involve evaluating the framework's completeness and usefulness for describing existing social machines. The goal is a shared understanding to advance research and development of these complex, evolving systems.