What is the difference between 3D and IMAX?

IN november open the first 3d theatre in my country, but iids no IMAX. Watching trailers, I see that the next Harry potter movie say "theatres and imax". Is the same or are competence in wich IMAX is a bran of �D movies and want all the market for themsevs and that movies are not used in others regular 3d cinemas, or doesn�t matter?