This is a new revised edition of a book which has come to be widely recognized as the best and simplest introduction available to Marxist economic theory. In a very lucid style, carefully defining all the technical terms used, it provides a comprehensive treatment of "the law of motion of capitalist society" which Marx expounded in the three volumes of origins of capitalism; surplus value; rent, interest and profit; capitalist accumulation; circulation of Capital and economic crisis; imperialism; distribution of the national product.
The perfect summarization of Das Kapital that a person could have. This book is a must-read if you wish to dive into the theories of Marxism. Imagine Marx but actually readable. This doesn't mean easy but more so less esoteric. EDIT: This is much more about the economics of Marxism rather than the philosophy of Marxism. Eaton sometimes brings up philosophical takes or basic (Marxist) historical analysis but it is mostly just economics (it is in the name of course!).