Data conversion can involve moving data from flat file systems to relational database management systems. It also can involve changing from systems with loose constraints to new systems with tight constraints. This chapter focuses on laying the groundwork for successfully executing a data conversion effort the first time around. The difficulties of a data conversion effort almost always are underestimated. Usually the conversion costs many times more than originally anticipated. Before embarking on data conversion, the data conversion team should decide whether data really needs to be converted and if it is feasible to abandon the noncurrent data. Starting fresh is an option. Once the data conversion team and the client have accepted the need for a conversion, the work can be planned in detail. The planning activities for conversion are standard in most respects and are typical of development projects.