Ecosystem service research has long been dominated by a monetary interpretation of value, neglecting other social perspectives on the importance of ecosystems for human well-being. Emphasis has been put on individual utility and rational choice, which does not adequately capture the full spectrum of social values of ecosystem services. A socio-cultural approach to value ecosystem services is increasingly advocated and is gaining more attention in the ecosystem service research agenda. The current documentation of socio-cultural perspectives on ecosystem services is, however, characterized by a conflation of the concepts of "cultural ecosystem services" and "socio-cultural values" of ecosystem services. This paper reviews (i) the concept of socio-cultural values within the ecosystem service framework, (ii) the social and ecological factors that determine socio-cultural values, and (iii) the methods by which socio-cultural values can be assessed. The clarifications of the concept of socio-cultural valuation and the structured listing of the available methods facilitate a better integration of socio-cultural values into ecosystem service assessments and help researchers to choose methods from the available portfolio.