While the importance of employee initiatives for improving the environmental practices and performance of organizations has been clearly established in the literature, the precise nature of these initiatives has rarely been examined (particularly the issue of their discretionary or mandatory nature). The role of organizational citizenship behaviour in environmental management remains largely unexplored. The main objectives of this paper were to propose and validate an instrument for measuring organizational citizenship behaviour for the environment (OCBE). Exploratory (Study 1, N = 228) and confirmatory (Study 2, N = 651) analyses were conducted to examine the factor structure of OCBEs. The factor structure that emerged from Study 1 indicated that the three main types of OCBEs were eco-initiatives, eco-civic engagement and eco-helping. The factor structure found in Study 1 was confirmed by Study 2. Analysis of the three types of OCBEs highlighted the complexity of discretionary initiatives for the environment in the workplace and points to a number of avenues for further research.