Chemical identity issues are of central importance to the successful implementation of Registration, Evaluation, Authorization and Restriction of Chemicals (REACH), both for the regulated community and for the European Chemical Agency (ECHA) responsible for REACH's implementation. A variety of nomenclature systems exists, some with similar naming convention but also with critically important differences. This book reviews the relevant chemical nomenclature issues in the EU and in the US and their impact on regulatory compliance. In particular, during the pre-REACH period, chemical identities frequently were described differently by different manufacturers for the same chemicals. The importance of having consistent nomenclature rules under REACH is related to the establishment of Substance Information Exchange Forums by ECHA after the pre-registration process, and, ultimately, industry consortia to meet registration requirements. If consistency is not established, there is a substantial risk that multiple registrations for the same substance will occur in conflict with the "One Substance, One Registration" principle under REACH. This book will discuss the relationships between and among various nomenclature systems and how chemical identity issues are to be addressed under REACH, along with comparative examples of chemical issues under TSCA in the US.