Begin with naptime. Introduce him to his crib during the sunny daytime, when you're nearby, to exorcise whatever nighttime demons he thinks are lurking there.
Bring the crib to him. Put the crib in your room so he gets used to the idea and feels secure knowing that he can still see you. After a few days, move him into his room.
Hang out. He may balk when you put him in the crib, so stay close, rubbing his back or singing him a lullaby. Gradually decrease the time you stay by him to help him learn to fall asleep on his own.
Sleep over. If your baby seems really terrified when you put him down, consider sleeping in a sleeping bag on the floor of his room for a few nights until the fear passes.
Give him a sniff. Since babies are comforted by their mom's scent, tuck him in with a piece of your old shirt so his crib will smell like you. As a precaution, remove it from the crib once he's asleep.