Book excerpt: This volume consists of papers developed from a joint ACE/ISSI symposium at the occasion of the eightieth birthday of Johannes Geiss. The symposium explored insights into the composition of solar-system and galactic matter that have been brought about by recent space missions, ground-based studies, and theoretical advances. Coverage includes linking primordial to solar composition, planetary samples, solar sources and fractionation processes, and interstellar gas and Cosmic rays.