An adjustable height intervertebral implant for total, partial, or nucleus replacement of an intervertebral disc space includes an upper endplate for contacting a first vertebra, a lower endplate for contacting a second vertebra and a mechanism for moving the upper endplate with respect to the lower endplate so that once the implant is inserted into an intervertebral disc space, the implant can be expandable from a first insertion configuration to a second expanded configuration. The mechanism for moving the upper endplate with respect to the lower endplate preferably includes a plurality of telescopic gear sets. The telescopic gear sets may be directly connected to one another or may be indirectly connected to one another by, for example, a pinion gear.