When and when-not to install into the GAC?

General MS guidelines

1. no
2. no
3. no

GAC is really a repository for Microsoft common .NET libraries. Yes, they let developers use it too, but as a rule of thumb, if you don’t need GAC, don’t use it. keep things simple and local if it doesn’t hurt.

• I would consider GAC only for performance reasons, for example if you have some huge assemblies, try to place them into GAC and NGEN them. It should significantly increase performance. Microsoft does it for all standard .NET framework assemblies during installation (now you know why that installation takes so long). Paint.NET does it as well (to improve startup time of their app). However most of us don’t work on huge frameworks or photoshop competitors, so most of the time, performance gains from having assembly in GAC are minimal. Not worth giving up simple x-copy deployment.

• Some developers might use GAC to make sure that users with insufficient privileges can’t delete or modify their assemblies.

• For others it might be for versioning reasons but here you should really reconsider. I’m not going to repeat what has been already said, you can read here why.

And don’t forget that once you want to deploy into GAC, your installer will need administrator privileges, you can pretty much forget click-once deployment, etc…