This report is an output of the fourth research track (Track 4) of WERF's strategic asset management research program 'Asset Management Communication and Implementation' (SAM1R06). Track 4 addressed 'remaining asset life', and had the overall objective of contributing to the development of techniques, tools and methods for estimating residual life of wastewater assets. Track 4 research was planned to be undertaken in a staged manner, so as to provide a stepwise development of concepts and protocols. To this end, the research team has produced a synthesis of knowledge in relation to "end of life" and "remaining asset life," which is the subject of this report. Drawing on the literature and the knowledge-base of the research team and industry partners, information is presented on the range of factors that influence the life of the different asset classes involved in the provision of wastewater services. A taxonomy of asset life is also given, along with a critical review of the conceptual linkages between risk, asset management and remaining asset life. A review of techniques used to assess remaining asset life is also included, as well as a detailed 'state of the art' review of modeling tools and approaches. One of the key questions to be addressed in this initial stage of the research was the state of knowledge with respect to the estimation and prediction of remaining asset life, and if there is the capacity to translate between condition and performance data (e.g. the presence of significant defects) and the residual life of an asset. In this regard, this report builds on previous work undertaken by the research team into protocols for condition and performance assessments, as detailed in WERF (2007).