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What is the difference between a namespace and an assembly?

C# Fundamentals Basic Fresher1–2 Yrs Conceptual 1 min read

Quick Answer

A namespace is a logical grouping of type names to avoid clashes and organise code — purely a naming device, resolved at compile time. An assembly is the physical deployment unit — a compiled .dll/.exe with its own version and identity. One assembly can contain many namespaces; one namespace can span many assemblies.

A namespace is just a way to organise type names and prevent collisions — it's a compile-time concept, nothing physical. An assembly is the actual compiled artifact, a DLL or EXE, and it's what gets versioned and deployed and referenced. They're independent: one assembly can hold dozens of namespaces, and a namespace like System.Collections.Generic is actually implemented across several different framework assemblies.

  • System.Collections.Generic types live across several framework assemblies.
  • A using directive imports a namespace; a PackageReference/project reference brings in an assembly.
  • File-scoped namespaces (namespace X;) reduce nesting in modern C#.
  • Namespace ≠ folder, but matching them is a strong convention.
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