This paper develops a model for the assessment of the maturity of the compliance function of investment firms. The model indicates a path of evolution wherein the compliance function matures from being reactive and inconsistent to becoming a proactive and integrated part of a firm’s business practices. A preliminary case study approach is used to test the practical application of the model in a Norwegian investment firm. The findings generally illustrate the ways in which the effectiveness of the compliance function can be evaluated using a maturity model. When it was used in the assessment of the compliance function within the case firm, the suggested model proved to be compatible with practice. The model represents an improvement framework that can help practitioners identify the status of the compliance function and provide guidance on its future improvement.