This volume contains the Lectures delivered at the X G.I.F.T.* International Seminar on Theoretical Physics on the subject ''Quantum Chromodynamics'' which was held at Jaca, Huesca, (Spain) in June 1979. The lecturers were J. Bartels, H. Fritzsch, H. Leutwyler, H. Lynch, E. de Rafael, and C. Sachrajda, who covered both theoretical and phenoraenological aspects of Q.C.D. Around 80 physicists attended the Lectures at the Residence of the University of Zaragoza in Jaca. The members of the Organizing Committee of the Seminar were J.L. Alonso (Zaragoza University), J. Bernabeu (Valencia University), c. Pajares (Barcelona Autonomous University), R. Tarrach (Barcelona University) and F.J. Yndurain (Madrid Autonomous University).