The regulation of the importation of new plant species underwent a major shift in the late 1990's with the implementation of the Hazardous Substances and New Organisms Act 1996. Under HSNO plant species entering New Zealand for the first time are assessed for their invasive potential. These risks are weighed against the benefits of importing the species. HSNO addresses the primary pathway for introduction of environmental weeds to New Zealand: intentionally imported horticultural species. This thesis explores the effectiveness of HSNO in regulating the importation of new plant species. The research focuses on the response of the nursery industry, a key target group, to the Act. Both qualitative and quantitative research methods are used to examine nursery industry views of the HSNO Act. Possible problems with noncompliance are investigated with the aid of a conceptual framework of policy design and compliance behaviour. The analysis suggests that targets may perceive the costs of compliance to outweigh the benefits thus undermining calculated motivations for compliance. The analysis also indicates that targets may perceive HSNO to be unfair and impracticable thus detracting from normative motivations for compliance. The implications of these issues for HSNO's effectiveness are discussed and means for addressing the problems identified are considered.