Zod has become the de facto standard for runtime validation in TypeScript projects. This article explores how to define schemas, infer types, and integrate validation at API boundaries. We cover primitive types, complex objects, discriminated unions, refinements, transforms, and how to compose schemas for reusable validation logic. We also discuss error handling strategies, custom error maps, and how to share schemas between client and server. Whether you are building REST endpoints, GraphQL resolvers, or form validation, Zod reduces the gap between compile-time types and runtime data, eliminating a whole class of bugs.