MU+-MU- COLLIDERS - POSSIBILITIES AND CHALLENGES

The current status of the mu+mu- collider concept is reviewed and discussed. In a reference scenario, a high-intensity pulsed proton accelerator (of K-factory class) produces large numbers of secondary pi's in a nuclear target, which produce muons by decay. The muons are collected and cooled (by ''ionization cooling'') to form high-intensity bunches that are accelerated to high-energy collisions. High-luminosity mu+-mu- and mu--p colliders at TeV or higher energy scales may be possible. Challenges in implementing the scenario are described. Possible variations in muon production, accumulation, and collisions are discussed; further innovations and improvements are encouraged.