This paper raises the question of how to guide the development of an emerging complex socio-technical system. The empirical basis for the discussion is a study of Vessel Traffic Services (VTS). We analysed the current state and the history of the service in Finland in four studies and identified several development needs. The results showed that there are differences between the outcome, practices and conceptions of the core task across different experts in the VTS centres, which can be explained by the current state of the constituents and the history of the activity system. Qualitatively different development phases characterised either by a top-down standardisation or bottom-up construction process were recognised. A combination of these processes was suggested for the future development strategy of the VTS. This could allow both continuous development within VTS and recognition of the need for a new system. A promising way to achieve continuous development is by creating reflective practices supported for instance with annual simulator exercises aimed at procedure development. We conclude that solving the current problems and promoting the development of the complex system call for a dynamic, open vision of the target future of the system, in which the pressures from the social, political and technological environments are taken into account. The results of ergonomics studies can help in self-reflecting, envisaging and developing supportive methods for the system but the persons within the system create the will to develop and find their way towards the development horizon.