object identification

ok so i have a 3D world, and i want the user to be able to point to an object on the screen (like a cube) and the computer to be able to realize that they are pointing at that object. what is the best way to do this? i assume lots of matrix multiplication with the mouse coordinates and the objects absolute position in 3D space?? thanks for any help

Read up on selection (in the Red Book if you have it).