From July 3 through July 21 of 2017, ConsenSys Diligence conducted a security review of the 0xProject's contract system. The findings and recommendations are presented here in this report. The 0x team on July 28 presented an updated system for ConsenSys Diligence to review. On August 3, a final system was presented and a draft version of this report was published the next day. This final report is published on August 15.