In offshore hydrocarbon developments subsea production systems become a more and more favoured alternative. Their ability to develop remote and marginal resources as well as increased freedom in placement of subsea wells compared to traditional systems is appreciated. For economic reasons the trend is to place sub-systems along the production chain increasingly subsea. However, intervention, maintenance and repair activities associated with such installations are costly. System reliability is therefore of great importance. This thesis describes subsea production systems, feasible maintenance strategies and gives an insight in reliability assessment. Based on a literature study a definition of subsea productions systems is given and their purposes and components are described. Ways for monitoring the system’s state and the one of single components, respectively, are pointed out. Furthermore, the role of subsea production systems in the development of offshore hydrocarbon resources is outlined and their importance for project investment decisions highlighted. This thesis furthermore presents an overview of maintenance concepts for and their employment on subsea production systems as well as failure prone items and common failure modes. Additionally maintenance organisation and activities as practised in the industry are featured. An analysis quantified the reliability of the safety function “Isolate the subsea well from the flowline by closing the production master valve”. Therefore a fault tree was developed to picture basic events and their interdependence in leading to possible failure of the function. The calculated average frequency of dangerous failures per hour was 8.56 x 10^-6 over a mission time of 20 years. This resulted in a safety integrity level of 1 therefore fulfilling the requirement of the industry standard. From the contributors to this result propositions for how to monitor the system in order to ensure the realisation of the system’s inherent reliability could be deduced. The monitoring of the pressure regulator, the subsea umbilical termination assembly, the surface pilot valve, and electric and electronic components was therefore suggested.