This International Standard provides guidance for the use of the new series of International Standards named Systems and software Quality Requirements and Evaluation (SQuaRE). The purpose of this Guide is to provide a general overview of SQuaRE contents, common reference models and definitions, as well as the relationship among the documents, allowing users of the Guide a good understanding of those series of standards, according to their purpose of use. This International Standard also contains an explanation of the transition process between the old ISO/IEC 9126 and the ISO/IEC 14598 series and SQuaRE.The SQuaRE series of International Standards is intended for, but not limited to, developers, acquirers and independent evaluators of systems and software products, particularly those responsible for defining systems and software quality requirements and for systems and software product evaluation. It is recommended that users of SQuaRE as well as ISO/IEC 14598 and ISO/IEC 9126 series of standards also use this International Standard as a guide to execute their tasks.