The world's top trainer, Mark Dvoretsky, and one of his best-known pupils, grandmaster Artur Yusupov, present a five-volume series based on courses given to talented young players throughout the world. The books contain contributions by other leading trainers and grandmasters, as well as games by pupils who have attended the courses. The main theme of volume 4 is "prophylaxis", a concept first expounded by Nimzowitsch and one which has brilliantly developed by Mark Dvoretsky and his pupils. The art of positional play is explained in terms of planning, manoeuvring, the study of typical positions, and deep strategy in grandmaster games.