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.

Inhalt
I: CMB and Large-Scale Geometry.- Physics of Cosmic Microwave Background Anisotropies and Primordial Fluctuations.- Cosmic Microwave Background Anisotropy Observations.- Weak and Strong Lensing Statistics.- II: Large-Scale Structure and Clusters.- Supermassive Black Holes and Galaxy Formation.- Galaxy Clusters as Probes for Matter in the Universe.- The Sunyaev-Zeldovich Effect: Recent Work.- Dark Matter from Weak Gravitational Lensing.- Baryons in the Diffuse Intergalactic Medium.- III: Galaxies and Components of Galaxies.- The Galactic Halo from Microlensing.- Clouds and Diffuse Baryonic Dark Matter.- Mass Distribution in Our Galaxy.- IV: Candidates for Dark Matter.- Quantum Field Theoretic Description of Matter in the Universe.- Axions.- Supersymmetric Relics.- Dark Quark Stars: Do They Matter for ?matter?.- V: Dark Energy.- Quintessence the Dark Energy in the Universe?.- VI: Dark Matter Detection.- Direct Detection of Dark Matter WIMPs.- Neutrino Mass and Oscillations.- Theoretical Aspects of Dark Matter Detection.- VII: Element Abundances.- Big Bang Nucleosynthesis Calculation.- The Primordial Helium-4 Abundance Determination: Systematic Effects.- Heavy Elements and Age Determinations.- VIII: Conclusions.- ?M Different Ways to Determine the Matter Density of the Universe.- Baryonic Matter and Dark Energy.- Author Index.