The paper first explains the significance of the complex of human capital and investments in human capital in terms of the comprehensive application of the scientific results in the production process. This is followed by the basic economic analysis of the importance of explicit knowledge and tacit knowledge for the development of enterprises and individual economies. After reviewing the role of certain forms of research and development in the creation of economic value, the accent is placed on the understanding of knowledge as the component of human capital in the economic growth model. It is pointed out that in contrast to the neoclassical models that stress the importance of the process of physical capital accumulation, in models of endogenous growth the source of growth is in the process of knowledge accumulation. Endogenous growth models recognize the existence of knowledge that is not mere public goods, i.e. that has the status of the market goods. This means that some knowledge is not fully accessible to all market subjects. It refers to knowledge which is protected by various forms of intellectual property or is potentially inaccessible for use by the interested entities. Such knowledge can be treated as the production factor equal to the physical capital, which has its appropriate market structure.