This project was an experimental and analytical study of pre-stressed composite beams. The type of beam studied consisted of a prestressed steel beam with a concrete slab attached to its top flange by means of shear connectors. The steel beam itself consisted of a rolled steel beam prestressed by rneans of a high strength steel cable attached to the bottom flange. Three beams were built and tested to failure, and the experimental results were compared with calculations based on existing theory. In addition, an analytical method for predicting the ultimate load of a prestressed composite beam was developed and predictions based on this method were compared to the experimental results.