In essence, Data Migration is about transitioning data from one system to another. The intention of this book is to provide an approach that achieves this in a robust, manageable and auditable way. Enhancing the traditional "Extract - Transform - Load" (ETL) methodology, a framework is introduced which incorporates, from the ground up, techniques to address common failings in data migration projects and processing. These techniques include a strong focus on auditability, reconciliation, monitorability, reuse and the ability to fine tune the cutover process.