This volume, the fourteenth in the Space Sciences Series of ISS/, is dedicated to the matter in the universe, which was the topic of a workshop organized by ISSI from 19 to 22 March 2001 in Bern. The aim of the meeting was to gather ac- tive researchers from various fields (cosmology, astrophysics, nuclear and particle physics as well as space science) to asses the exciting new developments in the search for abundant and yet unknown forms of matter in the universe. Due to the importance of the field and the rapid developments which are taking place ISSI decided to organize a workshop on matter in the universe and invited nine convenors, John Ellis, Johannes Geiss, Philippe Jetzer, Heinrich Leutwyler, Klaus Pretzl, Rafael Rebolo, Norbert Straumann, Gustav Andreas Tammann and Rudolf von Steiger, who formulated the aims and goals of the meeting. The work- shop was organized such as to have only plenary sessions with typically half- hour presentations and ample time for discussions. The last day was devoted to conclusions and future objectives. The knowledge of the amount and nature of matter present in the universe is undoubtedly one of the most relevant topics oftoday's astrophysics and cosmology.