In June 2012 the WCO Council adopted a completely updated version of the “WCO Guidelines on Post-Clearance Audit (PCA)”, which reflects the Members’ growing need to secure revenue while facilitating legitimate trade, and also the emerging migration of Customs activity away from border controls to the post-clearance environment in the context of trade facilitation. PCA is the most effective tool for many aspects of Customs controls, including application of the WTO Valuation Agreement, and for enabling an effective Customs risk management cycle by measuring traders’ overall compliance and reflecting the results for future controls. In the aforementioned Guidelines, the WCO has defined the PCA process as a “structured examination of a business’ relevant commercial systems, sales contracts, financial and non-financial records, physical stock and other assets as a means to measure and improve compliance.” It has been noted that Customs administrations have introduced audit control systems which differ in scope, authority and methodology. Also, the commercial environment differs between countries and it is recognized that compliance-based audit systems are difficult to introduce where there is a high incidence of informal trade. Nevertheless, Members are encouraged to work towards aligning their practices with the Guidelines, in order to ensure that they are using an approach which was developed from Members’ experiences and is consistent with modern Customs techniques. In order to achieve this goal, this Diagnostic Tool has been designed to assist managers and senior officials in Customs administrations, as well as external diagnosticians, in respect of the identification, design, implementation and evaluation of appropriate capacity building projects. This Tool has been developed under the WCO’s Revenue Package programme, and forms part of the WCO Customs Capacity Building Diagnostic Framework. The Tool should be used together with the PCA Guidelines and other relevant guidance material, particularly in the field of Customs risk management