The 1979 Cargese Summer Institute on Quarks and Leptons was organized by the Universite Pierre et Marie Curie, Paris (M. LEVY and J.-L. BASDEVANT), CERN (M. JACOB), the Universite Catholi~ue de Louvain (D. SPEISER and J. WEYERS), and the Katholieke Universiteit te Leuven (R. GASTMANS), who, like in 1975 and 1977, had joined their efforts and worked in common. It was the 20th Summer Institute held at Cargese and the 5th one organized by the two institutes of theoretical physics at Leuven and Louvain-la- Neuve. This time, the school was dominated by the impressive advances which were made in the field of perturbative ~uantum chromodyna- mics and its applications to high energy phenomena involving strongly interacting particles. The unification of weak and electromagnetic interactions being well established, a new picture in particle physics emerges wherein a possible unification of weak, electromagnetic, and strong forces is put forward. Its conse~uences were also discussed in detail. Finally, to complete the picture of the present status of high energy physics, experi- mentalists from the major laboratories around the world reported on the latest developments in electron-positron scattering, neutrino induced reactions, and hadron collisions. We owe many thanks to all those who have made this Summer Institute possible! Thanks are due to the Scientific Committee of NATO and its President for a generous grant and especially to the head of the Scientific Affairs Division, Dr. M. DI LULLO for his constant help and encouragements.