We investigate the design of harm-based and act-based sanctions for environmental offences. Empirical evidence concerning both criminal and administrative sanctions for Belgium clearly shows that the determination of harm-based and act-based sanctions for environmental offences is less straightforward than theory predicts. In criminal cases, harm-based sanctions are influenced by offence-related factors and specifically by the environmental harm caused, while the level of act-based sanctions is found to be independent of offence characteristics. Further, offender characteristics have a similar impact on both types of sanction, with the exception of the treatment of corporate offenders. In administrative cases, both types of sanction positively depend on the seriousness of (potential) harm caused. We find that sanctions increase for repeat offenders and decrease for offenders who took actions to minimize (potential) damages. Moreover, the analysis provides evidence of multiple objectives pursued by enforcing authorities. While our results confirm the general insights from previous studies, they are innovative in the distinction made between harm-based and act-based sanctions.criminal and administrative law in most European member states, while the use of civil law is currently less developed. However, in some European countries such as the United Kingdom, civil sanctions are increasingly used as an alternative for criminal sanctions (Watson, 2005;Langpap and Shimshack, 2010). Therefore, enforcement systems can vary greatly between countries. In this contribution we focus on criminal and administrative sanctions for environmental offences in Belgium.In general, environmental sanctions are used in two types of circumstance: first, when an offence caused actual harm, and second, when an offence involved risky behaviour or potentially harmful acts without the actual occurrence of harm. Examples of the first category include the destruction of natural habitats, emissions of hazardous pollutants and soil contamination caused by illegal disposal of waste; while examples of the second category include missing documents such as maintenance or fire reports, producing goods or services with an inappropriate environmental permit and the inaccessibility of measuring points for water sampling. This division is closely related to the discussion regarding the punishment of 'abstract endangerment'. Abstract endangerment offences are punished because of the potential creation of risk and not because of the actual creation of risk or harm (Fissell, 2014). In the remainder of the text we call the two types of sanction associated with harmful and potentially harmful offences harm-based and act-based sanctions respectively.Both types of sanction have their strengths and weaknesses. We first look at the characteristics of actbased sanctions. The main strength of act-based sanctions is that they intervene at an early stage, i.e. before the harm is done. However, such an enforcement strategy can rapidly inflate the number of punishments i...