An improved apparatus and method of sliding window construction are disclosed. When moving in an open position, a sash member is guided for movement in a first plane generally parallel to the window frame opening. When moving toward closure, the sash is guided by rotatable glide members that simultaneously transversely move all four corners of the sash into closure under cam action of the glides, to uniformly compress a weatherstrip seal around the entire perimeter of the sash. The transverse movement between open and closed positions can be performed in a manner such that the general plane of the sash remains parallel to the first plane throughout the transverse movement phase. Means are provided for retainably maintaining the sash at discrete positions along the transverse path of the sash during closure.