Progress on μ+μ- colliders

Advantages and disadvantages of muon colliders are discussed. Recent results of calculations of the radiation hazard from muon decay neutrinos are presented. This is a significant problem for machines with center of mass energy of 4 TeV, but of no consequence for lower energies. Plans are outlined for future theoretical and experimental studies. Besides continued work on the parameters of a 4 TeV collider, studies are now starting on a machine near 100 GeV that could be a factory for the s-channel production of Higgs particles. Proposals are also presented for a demonstration of ionization cooling and of the required targeting, pion capture, and phase rotation RF