The new muon storage ring at Brookhaven is intended to measure the anomalous magnetic momenta&mgr;of the muon to sub ppm accuracy. A preliminary run in 1997 gavea&mgr;=1&hthinsp;165&hthinsp;925(15)×10−9in agreement with previous CERN measurements. The principles of the experiment and numerous detailed improvements are described. ©1999 American Institute of Physics.