Those literary sources, which are about the interpretation of the working capital in a context with the financing strategies of the companies, about the related financial indices, and the counting methodological questions of all these, could not be called poor, nor unified. The deficiency of defining the concepts that give the theoretical basis and their vocational tenability, the controversial interpretation and the unclearness of the related methodological questions creates several problems. The problematic concepts are working capital, net working capital, working (operational) capital, the circulation of current assets and working capital management etc. The root of the problems could be found on the other hand in the unclearness of the theoretical contexts, in the deficiency and vocational tenability of the defining of the related concepts and categories. We define the concepts of working capital, net working capital, working (operating) capital based on the results of our several years of research work. We prove the theoretical basis of the concepts and we open up the causal connections, the interactions of the different elements, and we prove that the sectorial peculiarities cannot be separated from attention to defining the elements and the interpretation of the contexts.