Framework 1.0 was the first iteration. It was released in 2002 with Visual
Studio .NET.

Framework 1.1 is the second iteration and was primarily fixes from rushing
out .NET 1.0. It was released in 2003 with Visual Studio .NET 2003.

Framework 2.0 is the third iteration and changed the way things operate from
1.1. It was released in late 2005 with Visual Studio 2005.

Framework 3.0 is the fourth iteration, which sits on top of, rather than
replaces, Framework 2.0. It is a major release (left of decimal point)
rather than a minor (other side of decimal point) as it adds some major
components: WCF, WF and WPF primarily. It was released in late 2006, largely
without tool support (WF being the exception).

Framework 3.5 is the fifth iteration, which also sits on top of 2.0 (and
3.0), rather than replacing. It was released a bit earlier this month with
Visual Studio 2008.

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