  Very high energy cosmic rays are typically studied by measuring extensive air
showers formed by secondary particles produced in collisions with air nuclei.
The indirect character of the measurement makes the physics interpretation of
cosmic ray data strongly dependent on simulations of multiparticle production
in showers. In April 2002 about 50 physicists met in Karlsruhe to discuss
various aspects of hadronic multiparticle production with the aim of
intensifying the interaction between high energy physics and cosmic ray groups.
Current and upcoming possibilities at accelerators for measuring features of
hadronic interactions of relevance to air showers were the focus of the
workshop. This article is a review of the discussions and conclusions.
