The glass has to be out. It's super easy to remove just go ahead and do it. Just wait, get all your parts and you can do the dash pad, package tray, glass and headliner in one weekend. You CAN do a headliner with the glass in (if you have an experienced shop do it) but the second you remove the glass it will probably fall down. The glass out makes stretching the headliner easy. You also have to remove the weatherstrip retainers on each side of the car, which is easy as well. But like I said before I have never done either the headliner or a glass install before and I got them both on my first tries. The glass install was so easy it was almost funny.