Abstract: A greenhouse comprises a frame structure including base rails, eaves rails and a ridge rail. Upright wall posts extend into openings in the base rails and the eaves rails so that interengagement of those members prevents movement of the posts in either horizontal direction. Additionally, the ends of a transverse flange on such wall posts are received in notches in elongated lips on the base rail and eaves rail to limit pivotal movement of the wall structure until it is locked into its final position by the use of diagonal bracing members including length-adjusting mechanisms which, when moved into their locked positions, clamp the structural wall members in a unique predetermined angular orientation so ensuring ease of glazing. The roof sections are similarly constructed and novel one-piece eaves rails and a novel ridge rail further facilitate asssembly. The corner posts of the greenhouse serve to lock the side and end base rails together.