The GDPR defines a number of data protection principles in Article 5, for example, lawfulness or data minimisation as introduced in the previous chapter. Requirements for software development, and in particular for the software to be developed, follow from these principles. The current chapter provides an overview of the interpretation of the principles of data protection in the context of software development and IT and of the resulting requirements on software and its development. For example, in order to implement the principle of memory limitation, an erasure concept and the appropriate erasure functionality are required, both for structured and unstructured data.