In connection with arranging IAU Symposium No. 50 on 'Spectral Classification and Multicolour Photometry', sponsored by Commissions 45 and 25, it was decided to exclude all calibration problems. Instead it was agreed that we should attempt to arrange a separate symposium, dealing with the fundamental problems of the cali­ bration of absolute magnitudes and temperatures of stars. The Executive Committee of the IAU accepted our proposal, and IAU Symposium No. 54 was held in Geneva on September 12-15, 1972, sponsored by thefollowing IAU Commissions: 24, 25, 29, 33, 35, 37,44 and 45. It was attended by about 90 scientists representing 16 countries. The Symposium was divided into eight sessions. Each session started with a review paper by an invited speaker; this was followed by a general discussion including a few contributed papers. The contents of the present volume follow closely the programmes of the individual sessions of the Symposium. Most of the recorded discussions have been kept, and only in a few cases have the order of questions and comments been altered so as to obtain more homogeneity in the presentation.

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I / Absolute Magnitudes from Trigonometric and Statistical Parallaxes.- Absolute Magnitudes from Trigonometric and Statistical Parallaxes (Survey Lecture).- The Determination of Absolute Magnitudes from Proper Motions.- Note on Absolute Magnitudes in the Red and Infrared of Late M-Type Dwarfs.- Magnitude absolue moyenne des RR Lyrae.- A Program to Determine an Accurate Trigonometric Parallax for the Hyades Cluster.- II / Absolute Magnitudes from Galactic Clusters and Associations.- Absolute Magnitudes from Galactic Cluster and Associations (Survey Lecture - paper not submitted).- Attempt to Apply the U B V B1B2V1G Photometry to the Determination of the Distance of the Hyades.- A Far-Ultraviolet Flux Difference Between Hyades and Pleiades Stars.- Photo-Electric Measures of H? and H? in the Scorpio-Centaurus Association.- Rotational Effects on the Photometric Determinations of Absolute Magnitudes for A- and F-type Stars.- III / Calibration of Spectroscopic Parallaxes.- The Calibration of Luminosity Criteria (Survey Lecture).- Absolute Magnitudes and Colours of Field Giant Branch Stars.- On the K-line Width-Absolute Magnitude Relation.- Luminosity Calibration of Giants and Supergiants, G0-M5.- Calibration en magnitudes absolues de la classification BCD. Application à la détermination du module de distance du Grand Nuage de Magellan.- The (log g, log Teff)-Diagram, a Fundamental HR-Diagram.- IV / Absolute Magnitude Determinations from Hydrogen-Line Photometry.- Absolute Magnitude Determinations from Hydrogen-Line Photometry (Survey Lecture).- A Preliminary Test of the Calibration of the H? System in Terms of Absolute Magnitudes and Intrinsic Colours for Early-Type Stars.- Three-Dimensional Representation of A0-G5 Stars.- The H?-Absolute Magnitude Calibration.- Calibration of MK Types by Fitting the HR Diagrams of Three Moving Clusters.- Absolute Magnitudes of O Stars from a Study of Visual Multiple Systems.- V / Ground Based and Extraterrestrial Observations of Stellar Flux.- Ground Based and Extraterrestrial Observations of Stellar Flux (Survey Lecture).- Line Blanketing in Real Stellar Atmospheres.- Absolute Solar Intensities and the Solar Constant.- Absolute Calibration of Stellar Temperatures.- Comparison of Theoretical and Observed Indices for Three Photoelectric Photometric Systems.- First Results of the Absolute Calibration of the u, v, b, y System of Filters.- Radii and Fluxes of Long-Period Cepheids.- VI / The Use of Model Atmospheres for Temperature.- The Use of Model Atmospheres for Temperature-Gravity Calibration (Survey Lecture).- Ultraviolet Energy Distribution of He-Weak Stars.- The Absolute Magnitude and Stellar Population of a Ba ii Star.- VII / Stellar Temperature Scale and Bolometric Corrections.- Stellar Temperature Scale and Bolometric Corrections (Survey Lecture).- VIII / Choice of Standard Stars.- Remarks on the Photometric Criteria of Choice of the Standard Stars (Survey Lecture).- Determination of the Apparent V Magnitudes.- Distribution de l'énergie dans le spectre ultraviolet de quelques étoiles.