The last few decades have been called the Golden Age of Astronomy . The rapid increase of knowledge in the field necessitates publishing a new edition of the Astronomy and Astrophysics volumes of the Landolt-Boernstein. The title is now Astronomy, Astrophysics, and Cosmology . Cosmology has been added in order to make allowances for the increasing role of extragalactic astrophysics and cosmology. The present volume VI/4A on Instruments and Methods is the second to be published of the new series, following Volume VI/4B on the Solar System . Additional volumes on Stars , the Galaxy , Galaxies, Large Scale Structure and Cosmology are in the planning stage. The previous sections or volumes covering Instruments and Methods appeared in 1965, 1981 and 1993. Since then the astronomical instrumentation across the entire electromagnetic spectrum has evolved rapidly. This volume presents a description of the state of the art of the field. Another important new aspect is the inclusion of astronomical instrumentation outside the electromagnetic spectrum, with chapters on cosmic ray detectors, neutrino detectors, and gravitational wave detectors. The present volume is completed by a chapter on astronomical reference systems.