A collapsible and expandable interbody fusion cage primarily for use between adjacent vertebrae is designed to be collapsed so as to require the smallest opening necessary for insertion. An upper body is connected to a lower body by articulated supports. In the collapsed position, the articulated supports are folded inward between the upper body and the lower body. Once inserted, the fusion cage can be expanded to its fully open position to maintain spacing between adjacent vertebrae. The fusion cage is maintained in its fully open position by an overcenter latch. Bone material can be inserted in the space formed by the fully open fusion cage to aid in the fusion of the adjacent vertebrae.