Members of the Academy can nominate any number of movies. There are currently (and usually) a little below 6000 academy members. Members are usually previous years academy winners or nominees from all the categories, acting, production, script, music, technicians etc. Anybody can nominate up to any number of movies. Then the top five most nominated are selected, and secret poles are held near oscars, in which again all of the members of academy vote. The movie which gets most of the votes in this phase, is awarded the best movie of the year.