On modern Windows versions, do not manually download the installer unless you’re offline. Instead, enable .NET Framework 3.5 via Windows Features:

If you are on a computer without internet access or if Windows Update is failing, you can download the full standalone installer.

⚠️ Important Note: Windows 8, 10, and 11 require the Offline Installer (often called the ".NET 3.5 Service Pack 1 Full Package"). The standard web installer usually fails on modern Windows versions because it tries to fetch files that are no longer hosted correctly for legacy OS paths.

Official Microsoft Download Link:

How to use the Offline Installer:

Yes. Fully compatible. Use the Windows Features dialog or DISM method.

These versions have .NET 3.5 as an optional Windows feature (not a separate installer). Enable it via:

If you need the offline installer for older Windows versions:

There are two ways to install this framework on Windows. The best method depends on your internet connection.

Microsoft does not recommend downloading offline installers from third-party mirror sites. Always use the official Microsoft sources.