Internal Access

The internal access modifier draws a line around an assembly. Anything marked internal is visible to every type in the same compiled DLL, and invisible to every type outside it. That single rule does most of the work of separating a library's public contract from the helpers, caches, validators, and intermediate types that exist only to make the public contract work. This lesson covers how internal behaves in practice, the comparison with the other access modifiers at the assembly boundary, the [InternalsVisibleTo] attribute that lets a test project see internals without weakening them for everyone else, and where the seams between projects sit in a typical .NET solution.