Automating business processes across a network of untrusted business parties are increasingly problematic due to the inherent lack of mutual trust between parties. Blockchain provides a promising solution to enact business processes in a trustworthy manner in untrusted business environments. Blockchain includes a shared ledger that provides a trusted, privacy-preserving, immutable data repository that can store business objects and events, enabling provenance and transparency. It also supports the decentralized execution of computations on it in the form of programs called smart contracts. This chapter describes the role of the smart contract and shared ledger in automating collaborative business processes. In particular, we present a meta-model, a life cycle model, and a reference architecture for smart contract-driven business transactions and processes.