The introduction consists of an essay on the development of chess problems, how "two main types o accumulation have marked the process of composition during the last fifty years: on the one hand, the pursuit of variations, that is the accumulation of different elements in one problem; and, on the other hand, the pursuit of echoes, that is the accumulation of similar elements in one problem". 300 problems (100 sets of 3) are devoted to these 'tasks' and 'echoes', grouped under 21 main thematic ideas, and discussed, with solutions.