Why Func<T,bool> instead of Predicate<T>?

While Predicate has been introduced at the same time that List<T> and Array<T>, in .net 2.0, the different Func and Action variants come from .net 3.5.

So those Func predicates are used mainly for consistency in the LINQ operators. As of .net 3.5, about using Func<T> and Action<T> the guideline states:

Do use the new LINQ types Func<> and Expression<> instead of custom delegates and predicates

I've wondered this before. I like the Predicate<T> delegate - it's nice and descriptive. However, you need to consider the overloads of Where:

Where<T>(IEnumerable<T>, Func<T, bool>)
Where<T>(IEnumerable<T>, Func<T, int, bool>)

That allows you to filter based on the index of the entry as well. That's nice and consistent, whereas:

Where<T>(IEnumerable<T>, Predicate<T>)
Where<T>(IEnumerable<T>, Func<T, int, bool>)

wouldn't be.