An expandable interbody spacer (IBS) device designed to restore the disc height between vertebral bodies. The expandable interbody spacer device has an integral, moveable expansion member or spreader, provided between two plates. The plates are connected by one or more connecting members that retain the plates in a position proximate to one another while allowing the plates to move from a first unexpanded position to a second expanded position upon activation of the expansion member. According to aspects of the invention, the interbody spacer device can be implanted in an unexpanded or collapsed configuration, and then expanded to full height by engaging the expansion member. In other embodiments, the interbody spacer device may take various forms, for example, it may be cashew, rectangular or annular.