Business process modeling and enactment are notoriously complex, especially in open settings, where business partners are autonomous, requirements must be continually finessed, and exceptions frequently arise because of real-world or organizational problems. Traditional approaches, which attempt to capture processes as monolithic flows, have proven inadequate in addressing these challenges. We propose (business) protocols as components for developing business processes. A protocol is an abstract, modular, publishable specification of an interaction among different roles to be played by different participants. When instantiated with the participants' internal policies, protocols yield concrete business processes. Protocols are reusable and refinable, thus simplifying business process design. We show how protocols and their composition are theoretically founded in the phi;-calculus.