Which .NET framework version will be used when there are many installed?

If I have multiple versions of the .NET framework installed on a 开发者_JAVA技巧machine, will the newest version be used?

Will a .NET app use a specific version of the framework depending on how it has been programmed?

.NET applications specify via their CLR header what version of the runtime they require in order to run. The ability to build and run against different versions of .NET is supported in Visual Studio through the multi-targeting feature.

It's a property of each project (csproj).
You can modify it in the "Application" tab, under "Target framework"

It's all about the application it self, the developer choose what is the suitable Framework that he/she wants to program against

Then, when creating the Setup Project to deploy the application, there is a flag that tells to install that Framework version, if clients does not have it already

This is valid to any .NET application

We developers tend to think:

Do I need the new features of the newest framework?

cause this will install new package in the client, and sometimes we really don't need and assuming everyone has Vista / Windows 7, .NET 3.5 is already there, so we go for 3.5