IQueryable vs IQueryable<T>

Question

I'm simply wondering why there is a IQueryable<T> version without the generic capability ?

Answer 1

The generic IQueryable<T> is the one you use most often in method signatures and the like. The non-generic IQueryable exist primarily to give you a weakly typed entry point primarily for dynamic query building scenarios.

by Matt Warren from LINQ: Building an IQueryable Provider - Part I

You should use generic IQueryable<T> everywhere it's possible.

Answer 2

I imagine it's the same reason as Jon Skeet gives in Difference between IEnumerable and IEnumerable<T>? , to allow use in a foreach loop. IQuerable would be castable to IEnumerable, whereas IQueryable<T> would not.

Also see Marcin's answer about use in dynamic query building scenarios.