With the deep economic crisis we face since 2008 also the interest in Marxian theories increased worldwide. This was not really surprising: while in Marx’s economic theory crises play an important role, they are nearly neglected in mainstream economics. They appear there as mere accidents, which could be prohibited by flexible markets (this is the belief of neoclassical economists) or by an appropriate economic policy (the belief of the Keynesians). But talking about Marxian economic theory, we should always have in (...) mind, that there is a certain development in Marx’s thinking as well as there are certain ambivalences in basic theoretical concepts. In traditional Marxism, which mostly tried to present Marxian theory as a complete and perfect building, especially such ambivalences were often negIected or even denied. In the following I will give a short overview about the main stages of Marx’s theoretical development, and then I will focus on the ambivalences of Marx’s mature theoretical work. (shrink)