Protocol Buffers, or protobuf, are at the heart of designing gRPC services. You use protobuf to define the structure of your data, the messages exchanged, and the overall contract between clients and servers. This approach ensures that both sides understand exactly what data is being sent and received, regardless of the programming language or platform.

A protobuf file, typically with a .proto extension, describes your service in a clear, structured format. Within this file, you define messages—data structures with fields and types—and services, which specify the available remote procedure calls (RPCs) and the messages they use. This structure provides a single source of truth for your service contract, reducing misunderstandings and making collaboration easier.

Versioning is a crucial concept in protobuf. As your service evolves, you can add new fields to messages or new RPC methods without breaking existing clients. Protobuf supports backward and forward compatibility, giving you the flexibility to update your services while maintaining stability.

Using protobuf with gRPC brings several benefits. You gain efficient, binary serialization for fast communication, automatic code generation for multiple languages, and strong typing for reliable data exchange. This combination leads to clear, efficient, and robust APIs that are easy to maintain and scale.