The Decomposable Monolith is a software architecture pattern proposed by Paul Dix, which suggests starting new projects as monolithic applications to take advantage of faster development and iteration cycles, while also allowing for easier transition to service-based designs later. The key advantages of this approach include reduced communication and documentation overhead within the team, faster setup, testing, and debugging, and the ability to easily break out individual components into services when needed. To implement this pattern, Paul Dix proposes designing a monolithic application with a modular structure that allows for easy decomposition into services, using interfaces and structs to define the boundaries between components, and creating thin wrappers around other well-known projects or services to ensure compatibility and scalability. The goal is to create a system that can be easily maintained and updated while still providing the benefits of both monolithic and service-based architectures.