Yes, INCLUDING is a Scrabble word!

Letter values in Scrabble US: I 1, N 1, C 3, L 1, U 1, D 2, I 1, N 1, G 2.

Is it a valid word?

INCLUDING is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

have as a part, be made up out of
consider as part of something
add as part of something else; put in as part of a set, group, or category
allow participation in or the right to be part of; permit to exercise the rights, functions, and responsibilities of

Also: let in.