In what order do you list souces in a works cited list using MLA?

I am doing a research paper for my English cl, and I am ready to make the works cited list, however I don't know what order to put them in. Do they go in the order they appeared in the paper, or in alphabetical order, and it they are in alphabetical order, is it by first or last name. I have spent 20 minutes looking through my text book and cant find the answer.