The main objective of the thesis is to analyse the development and structure of civil service careers in small and large states, taking Estonia and the United Kingdom as case studies. In the first part of the thesis, different disciplinary perspectives on careers are examined, including public administration, management, organisation theory, labour economics, sociology and psychology. A distinction is made between career, job and network systems in civil services, as frameworks for career development. Careers are analysed from two perspectives: individual and institutional. Mobility within and between organisations is given special attention, leading on to an investigation of boundaryless careers. The findings from different perspectives are drawn together to develop an integrated approach to civil service careers. The thesis also takes account of broader societal changes that have substantially affected the understanding of careers in the 1990s by increasing their diversity. The case studies in part two draw on documentary materials and interviews with civil servants in the United Kingdom and Estonia to identify similarities and differences in the characteristics of the development of careers in these two countries. The thesis shows how the reforms in the British and Estonian civil services in the 1990s have affected the way in which institutional and individual careers have evolved. An important objective of the thesis is to analyse how the size of states influences career opportunities and structures. In part three differences between larger and smaller countries are shown to be not merely quantitative but also qualitative. The size of the state appears to have a number of implications for the development of civil service systems and for career management within them. The findings suggest that traditional bureaucratic models may not be well suited to the small state context, as smaller institutions may have difficulty in developing stable structures with formalised career paths. Network organisations can, however, offer an opportunity for small states to develop further their civil services by providing a large degree of flexibility in career management.