Karl Marx set about to analyze the development of capital, the components of capital and the modern day application of capital. As a political economy scientist he outlined the key human ingredient; the concept of the 'surplus value of labor'. This concept is the most difficult to understand of the three essential elements of what we now call Marxism, but it is the most important. As well, this work is the most important contribution of Marx to the world of political economy. Regardless of one's political and economic views it is necessary to comprehend what is put forward by Karl Marx's Das Kapital in order to have knowledge of how capital is created and used in the production of all goods and services. Of the 50 books I have published to date, Das Kapital is the best seller in the USA and the UK.