Dedicated to Alan Barrett, formerly of MIT (Massachusetts Institute of Technology), this text updates current understanding of the composition and dynamics of interstellar matter. Thirteen invited papers and 42 poster papers discuss molecules as probes of cloud chemistry, molecules as probes of cloud physics, grains and large molecules and new techniques for studying interstellar matter. The career of Alan H.Barrett as a scientist, colleague and teacher is set in context and the future implications of his work are discussed.

Table of Contents:
Part 1 Molecules as probes of cloud chemistry: the chemistry of diffuse clouds, A.Dalgarno; newly detected molecules in dense interstellar clouds, William M.Irvine et al; the chemistry of shocks and outflows, W.J.Welch. Part 2 Molecules as probes of cloud physics: heating and cooling of molecular clouds and their surfaces, David Hollenbach; structure and motions in molecular clouds, Bruce G.Elmegreen; the evolution of molecular clouds, Frank H.Shu and Susana Lizano. Part 3 Grains and large molecules: molecular observations - molecular chains and rings, the cologne 3-m radio telescope on Gornergrat, G.Winnewisser; the size and composition of interstellar grains, John S.Mathis; "infrared cirrus" - new light on the interstellar medium, Michael G.Hauser; magnetic alignment of grains, Roger H.Hildebrand. Part 4 New techniques for studying interstellar matter: millimeter and submillimeter interferometry, D.Downes; submillimeter and far-infrared detectors, T.G.Phillips; large millimeter and submillimeter telescopes, Richard Hills. Part 5 Contributed papers: radiative transfer through molecular clouds - P-Cygni profiles, Lawrence H.Auer et al; gravitational collapse of cloud cores - two candidates, Eric R.Keto et al; magnetic fields in molecular clouds - how supportive are they under pressure? Alyssa A.Goodman et al; a reduced role of the magnetic field in the dense core regions of the Taurus clouds, Mark H.Heyer; detection of v=0, J=1 - O silicon monoxide absorption in Sgr B2 and observations of silicon monoxide at 43.423 GHz in HII regions, A.D.Haschick et al; SiO J=1 - 0 emission near the galactic center - tidal stripping and shocks? Bruce L.Jacob et al; ammonia observations in the region NGC7023, Cecilia P.Benton; dense cores associated with Herbig Ae/Be stars, J.Gregory Stacy et al; a source model for the molecular core of L134N, Daryl A.Swade and F. Peter Schloerb; water emission in Orion at 183 and 380 GHz, M.A.Frerking and T.B.H.Kuiper; far-infrared, rotationally excited OH emission in Orion-KL, Gary J.Melnick et al; 40"-resolution CS maps of the core of the Orion molecular cloud, John C.Szczepanski and Paul T.P.Ho; the duplicity of the "protostar" IRAS16293-2422, Alwyn Wootten; a composite CO survey of the entire Milky Way, T.M.Dame et al; aperture synthesis observations of CO in the starburst galaxy NGC2146, James M.Jackson; molecular outflows in galactic nuclei, Willem A.Baan and Aubrey D.Haschick; the cepheus-A and mon-R2 outflows; 15" resolution maps, John Bally et al; L43 - an example of the interaction of molecular outflows and dense cores, Robert D.Mathieu et al; high resolution radio observations of the region near HH 7-11 - outflows and disks, Alexander Rudolf; precise observations of HH 7-11, Toshiaki Takano. (part contents)