Human relationships with nature are increasingly being recognized as an important factor in environmental conservation. Understanding how people perceive and know nature, and the language they use to describe nature, their concepts of nature, could have important implications for conservation policy and management. This empirical research sought to examine and categorize concepts of nature, and explore how such thoughts relate to connection with nature and conservation behaviors. Multidimensional scaling revealed three concepts of nature categories: descriptive (e.g., plants, animals, landscapes), normative (e.g., conservation, balance, life), and experiential (e.g., activities in nature, positive emotions, aesthetic qualities), plus a complex category (two or more of the descriptive, normative, or experiential categories). Connection with nature scores (total and dimensions) were higher among participants who described nature in experiential or complex terms than those who described nature in descriptive terms. Participants who described nature in experiential terms were more likely to have participated in environmental volunteering, citizen science, picking up litter, and community gardening in the past year than those who used descriptive terms. Concepts of nature moderated the relationship between the connection with nature and picking up litter. These results may usefully inform conservation policies and campaigns intended to increase connection with nature and participation in conservation behaviors, through the use of language emphasizing experiential and more complex concepts of nature, by encouraging personal reflection on one's experiences of nature, and through the design of natural spaces that encourage active engagement with nature.