Concepts like values, attitudes, and perceptions have successfully been used in environmental psychology to describe environmental perception and behavior. Nevertheless, this dominant individualistic paradigm has been challenged from more constructivist approaches, like discursive psychology. In an attempt to find cross-fertilization between the different theoretical fields, social representation theory (Moscovici 1961/1976) has been put forward in both social- and environmental psychology (e.g. Castro 2006). Social representations describe how different groups of people develop specific understandings (including knowledge, values, and metaphors) of an object and how they use such understandings to constitute a common reality. Social representations are socially constructed and facilitate communication by presenting a more or less commonly shared set of representations, needed to understand the signs people attach to concepts and objects (Wagner et al. 1999). Social representations can be studied on both the individual, as well as the social level. This study focuses on the individual level. Social representations of biodiversity, landscape and nature are investigated, focussing on differences between experts and lay people. To study both the structure as well as the content of these representations, a word association task has been administered to 100 experts in the field of ecology and 200 people from the general public. Respondents produced free associations with the words biodiversity, landscape and nature. Differences in the occurrence of meanings between experts and lay people, as well in the structure of the social representations are described. Results have been analysed using correspondence analyses, resulting in six (3 x 2) twodimensional plots representing the structure of social representations of the two groups (expert-lay people) for all three concepts (biodiversity-landscape-nature). Additional to this open question, a semantic differential scale was included in the questionnaire, which allows more rigorous statistical analyses. Results are helpful to understand differences in meanings attached to biodiversity between experts and lay people and the anchoring of the concept of biodiversity in the related, and well-established, concepts of nature and landscape. Understanding these differences may improve communication on biodiversity related policies and facilitate communication with stakeholders in participation processes.