Reflexivity and its counterpart— anti-reflexivity— are key concepts in environmental sociology. Reflexivity and similar concepts are presented as means for taking constructive steps towards sustainability in face of the often wicked nature (complex, uncertain, dynamic, value-laden, dilemmatic, ambivalent) of socio-ecological problems and risks. Anti-reflexivity is the suppressing or resisting of reflexivity. This entry discusses definitions of reflexivity, anti-reflexivity and related concepts based on key scholarly work in environmental sociology. From this field of research, reflexivity— or its absence/resistance— is discussed with regards to the system or macro level (society at large, state apparatus, the scientific field or general discourses in the public sphere), the process level (governance networks, decision-making processes), or at the level of individual and collective choices of action (consumption/lifestyle choices, social movements).