The Sitges International School of Physics is the second one to be held in Spain on the Many Body Problem. The first one took place on Mallorca during the summer 1969. The aim of the school was mainly to direct the interest of professors and students of Spanish Universities tow rds this concrete field of re- search. For this purpose 55 specially prepared lectures were given by an eminent collection of lecturers. Besides, a school of this class contri- butes to the scientific formation of many students from other countries. Also, in a meeting of this kind, personal contacts are born that...