This guide is intended to provide an overview of the most important developments in the field of quantum technologies from the point of view of IT security, as well as recommendations for action for migrating to quantum-safe cryptography. The transition to quantum-safe cryptography leads to numerous open questions (for example, the selection of suitable algorithms, necessary adaptations to protocols and standards, and many more), which are discussed in this document. As a basis for this discussion, the possibilities and the state of development of quantum computers are roughly described first. Then, the document discusses post-quantum cryptography and quantum cryptography in detail and distinguishes between these two complementary proposals.