The Internet's growth, and the proliferation of online collaboration tools and platforms and the federated systems that support them, have enabled ad hoc processes in which people interact in a dynamic collective way. Such activities are characterized by their flexibility and data-driven nature, which makes them more difficult to analyze and support than traditionally rigid processes. Systems that handle dynamic collective work activities must address three main challenges: finding patterns in ad hoc execution behavior, handling concurrent users and concurrently executing tasks, and providing operational support. This special issue provides a snapshot of ongoing work in this area that addresses these challenges. © 2013 IEEE.