Abstract The thirty-fourth annual CALPHAD meeting was held at Kasteel Vaeshartelt, Maastricht, The Netherlands, on May 22–27, 2005. The local organizing committee consisted of Harry A.J. Oonk (chairman), Aad C.G. van Genderen, Michel H.G. Jacobs, Paul J. van Ekeren, and Marjan Hogenbirk (secretary); all employed at Utrecht University, Faculties of Chemistry and Geosciences. There were 134 delegates and 6 accompanying guests from 23 different countries. Oral communications (72) were presented in the following 10 sessions: 1. First Principles and Other Matters 2. High Pressure 3. Modeling and Experiments 4. CALPHAD Thermodynamics 5. Kinetic Matters 6. Miscellaneous (a collection of diverse subjects) 7. Experimental Thermodynamics 8. Nuclear Materials and Other Matters 9. Cluster Variation Subjects 10. CALPHAD Thermodynamics and Related Subjects. Posters (60) were exposed in a continuous manner from Monday morning to Thursday evening. The posters were largely divided into two groups with one group closely related to Calphad Thermodynamics: first principles; thermodynamic phase diagram analysis; algorithms for Gibbs energy minimization; and kinetics, and another group covering a variety of subjects: teaching; statistical thermo-dynamics; experimental determination of phase equilibrium relationships; (micro)-calorimetry; molar volume; viscosity; waste heat; and subjects from the realm of molecular alloys. After Monday’s last lecture, a lively plenary discussion took place—some kind of a game between (traditional) CALPHAD thermodynamics and first principles. The discussion was continued on Tuesday evening. The present summary is organized into three sections I. Summaries of oral communications II. Titles of the exposed posters III. Summary of the discussions on Monday and Tuesday evening.