This third course of the Blockchain series focuses on decentralized applications (Dapps), which provides anyone with access to blockchain features and services. Participants will use Truffle IDE, smart contracts, a simple web client and a MetaMask client. They will learn about the architecture of this application: the front-end client interface, backed by the blockchain and smart contracts. The course covers the basic design of a Dapp, Truffle development process and commands, test-driven development of Dapp, Dapp application models and emerging standards that are essential for predictable Dapp behavior.