High Energy Cosmic Ray Interactions – an Overview

The status of present theoretical description of very high energy hadronic interactions is reviewed. The impact of new results of accelerator and cosmic ray experiments on hadronic interaction model constructions is discussed in detail. Special attention is payed to remaining uncertainties in model extrapolations into the ultra-high energy domain, in particular, concerning model predictions for the muon component of extensive air showers. New promising theoretical approaches are outlined and future experimental prospects are discussed.