In June 1983 the Astronomical Institute of the State University of Groningen, founded by Kapteyn about 100 years ago, celebrated its one-hundredth anniversary. At the suggestion of its Chairman, R.J. Allen, the Kapteyn Institute invited the International Astronomical Union to mark the centenary by holding a Symposium on "The Milky Way Galaxy". The purpose of the Symposium was to review recent progress in the study of our Galaxy, to define current problems, and to explore prospects for future development. The Symposium programme would emphasize the large-scale characteristics of our Galaxy, and highlight both the historical development of our understanding of the Milky Way Galaxy and the importance of studies of external galaxies to this understanding. The Symposium was sponsored by four IAU Commissions: 33 (Structure and Dynamics of the Galactic System), 28 (Galaxies), 34 (Interstellar Matter) and 41 (History of Astronomy). The Scientific Organizing Committee, listed on page xviii, represented a broad range of nationalities and of expertise, including two historians of science. A meeting of the Committee, held during the IAU General Assembly at Patras, provided an excellent opportunity to discuss plan and format of the Symposium, topics and speakers; thereafter, the-Committee was regularly consulted by letter and telephone. IAU Symposium 106 was held at Groningen on 30 May - 3 June 1983, in the new building occupied by the Kapteyn Institute since January 1983. There were about 200 participants, coming from as many as 25 countries.

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Coloured Illustrations.- History of Galactic Research.- I The Milky Way from antiquity to modern times (R).- Kapteyn and statistical astronomy (R).- Studies of the Milky Way 1850-1930: some highlights (R).- The discovery of the spiral arms of the Milky Way (R).- II Composition, Structure and Kinematics.- II.I Galactic Constants, Rotation and Mass Distribution.- Models of the mass distribution of the Galaxy (R).- A model of our Galaxy (I).- Mass models of three southern late-type dwarf spirals.- The Galactic constants - an interim report.- Galactic rotation outside the solar circle.- Young galactic clusters and the rotation curve of our Galaxy.- How well do we know the rotation curve of our Galaxy?.- Galactic rotation and velocity fields.- II.2. The Stellar Component.- The old population (R).- Near-infrared studies of the Milky Way.- Infrared scanning of the Galactic bulge.- Infrared studies of the stellar population in Baade's Window.- On the nature of OH/IR stars.- The stellar disk component: distribution, motions, age and stellar composition (R).- Computer-based catalogue of open-cluster data.- The kinematics of nearby stars and large-scale radial motion in the Galaxy.- The Galactic radial gradient of velocity dispersion.- Stellar chemical-abundance gradient in the direction of the South Galactic Pole - preliminary results.- Star counts, local density and Kz (I)force.- The stellar distribution in the Galactic spheroid.- Studies of O-F5 stars at the Galactic poles.- Galaxy population structure from proper motions.- II.3. The Gaseous Component: Large-Scale Distribution.- Large-scale distribution and motions of gas.- Survey of Galactic HI emission at ?b? ? 20°.- The vertical distribution of Galactic HI: the Arecibo-Green Bank Survey.- New light on the corrugation phenomenon in our Galaxy.- HI at the outer edge of the Galaxy and its implications for Galactic rotation.- The electron density in the plane of the Galaxy.- Molecular clouds in external galaxies (I).- Comments on the distribution of molecules in spiral galaxies.- Distribution and motions of CO in M51.- CO (2?1) observations of Maffei 2.- CO survey of the Southern Milky Way.- Distribution of CO in the Southern Milky Way and large-scale structure in the Galaxy.- A CO (2?1) survey of the Southern Milky Way.- The carbon monoxide distribution in the inner Galaxy.- Outer-Galaxy molecular clouds.- CH in the Galaxy.- High-energy gamma rays and the large-scale distribution of gas and cosmic rays (I).- Large-scale mapping of the Galaxy by IRAS.- II.4. The High-Energy Component.- High-energy Galactic phenomena and the interstellar medium (R).- The high-latitude distribution of Galactic gamma rays and possible evidence for a gamma-ray halo.- On the ultraviolet background radiation of the Galaxy.- Radio continuum emission of the Milky Way and nearby galaxies (I).- Loop I (the North Polar Spur) region - a quasi radio halo.- The magnetic-field structure and dynamics of NGC 253.- Modelling the Galactic contribution to the Faraday rotation of radiation from extra-galactic sources.- A bisymmetric spiral magnetic field in the Milky Way.- II.5. Spiral Structure.- Spiral structure of the Milky Way and external galaxies (R).- Which kind of spiral structure can fit the observed gradient of vertex deviation?.- Spiral structure and kinematics of HI and HII in external galaxies (I).- A systematic study of M81.- Determination of Galactic spiral structure at radiofrequencies (R).- Giant clouds and star-forming regions as spiral-arm tracers.- The largest molecular complexes in the first Galactic quadrant.- Interpretation of the apparent anomalies of the Galactic structure.- II.6. Small-Scale Structure and Star Formation.- Small-scale structure and motions in the interstellar gas (I).- Atomic hydrogen towards 3C10.- Interferometric observations of the small-scale structure of Galactic neutral hydrogen.- A 10-GHz radio-continuum survey of the Galactic-plane region at the Nobeyama Radio Observatory - A complex region at ? = 22° ? 25°.- Interstellar sodium and Galactic structure. A high-resolution survey.- Molecular-cloud clusters and chains.- Three large molecular complexes in Norma.- Comparison of CO in the Galaxy and the Magellanic Clouds.- Star formation in the Orion Arm (I).- A survey of molecular clouds associated with young open star clusters.- A new study of the neutral hydrogen in Gould's Belt.- II.7. The Galactic Nucleus.- The Galactic Nucleus.- Fine structure of molecular clouds within 1 minute of arc of the Galactic Center.- Recombination-line observations of the Galactic Centre.- Are spiral nuclei "active" in the radio continuum?.- Phenomena at the Galactic Centre - a massive black hole? (I).- II.8. Outskirts and Environment.- Highlights of high-velocity clouds (R).- A deep survey for high-velocity clouds.- A survey for high-velocity clouds in the inner Galaxy.- Observations of high-velocity clouds colliding in the anticenter.- The Milky Way: a halo, a corona, or both?.- II.9. Comparison of Andromeda and Milky Way Galaxies.- A comparison of the Andromeda and Milky Way galaxies (R).- Radial distributions of constituents in M33, the Galaxy, and M51.- A coordinated radio and optical survey of M31.- Distribution and motions of HI in M31 (I).- The production of a 16-mm film of M31.- Distribution and motion of CO in M31 (I).- Large-scale maps of M31 at middle and far infrared wavelengths (I).- III Dynamics and Evolution.- III.1. Milky Way, Magellanic System and Local Group.- Slippery evidence on masses in the Local Group (R).- A collision between the Large and Small Magellanic Clouds 2×l08 years ago (I).- Tidal interactions between the Galaxy and the Magellanic Clouds.- III.2. Dynamics of the Disk.- Dynamical evolution of the Galactic disk.- Evolution of the vertical structure of galactic disks.- Heating of stellar disks by massive gas clouds.- Stellar velocity distribution in the presence of scattering massive clouds.- Warps and heavy halos.- 3-dimensional particle simulation of vertical oscillations in gas discs.- Two-fluid gravitational instabilities in a galactic disk.- Collective phenomena in a multi-component gravitating system (I).- III.3. Spiral Structure and Star Formation.- Formation and maintenance of spiral structure in galaxies (R).- Two-dimensional calculations of tightly wound spiral shocks.- Oscillations of rotating gas disks: p-modes, g-modes, and r-…