1/2 gallon milk (you can really use however much you like.
I used 1/2 gallon--maybe a bit more, because that's what fit in my crock pot, just make sure your milk and yogurt ratio match up)
1/2 C plain yogurt (for a starter, to get the process going)
1/4 C powdered milk. (optional) I know several people who add this to make it even creamier (especially if you are using a lower fat content milk)
crock pot
thermometer
blanket
colander and cheesecloth if you are going to make Greek yogurt