The article is devoted to the analysis of theoretical concepts and empirical characteristics of internal mobility of researchers. Internal mobility is understood as a changing job by moving from one university or research organization to another within the country as well as some forms of combining jobs - such as the consulting of professors in companies. Theoretical studies link the internal mobility with concepts of human and social capital and justify its positive influence on the knowledge transfer, growing qualification of researchers, and increase in innovative activity as a whole. Empirical assessments of the internal mobility show that it is positively connected with the productivity growth. However it cannot be stated that the internal mobility decisively influences the number of publications and patents. Internal mobility in Russia is lower than in developed and BRIC countries. It is especially true for the inter-sector mobility that implies movement of researchers from universities and research organizations to companies and vice versa. The low level of internal mobility may be explained by such factors as practice of hiring and career growth as well as a specific Russian phenomenon of inbreeding when universities mainly hire their own graduates. In order to clarify the current state of internal mobility, pilot interviews with researchers representing three sectors of Russian science - academy, university, and industry - were conducted, which has revealed that internal mobility is low in all sectors. Three major reasons were identified: mentality of leadership, low quality of workforce that specifically affects the inter-sector mobility and the high average age of Russian researchers in all sectors. The article concludes with some practical suggestions to policymakers aimed at increasing the internal mobility of researchers.