Security and privacy have become such important commodities in the information and globalization era that it would be extremely beneficial to comprehensively explore possibilities for providing (near-) perfect performance in these fields. A method based on quantum phenomena and the laws and limitations of quantum information processing and communication was recently developped with the aim of providing so-called unconditional security in sensitive cryptographic tasks. During the last 20 years, quantum cryptography has made remarkable –even previously unimaginable– progress. The goal of this paper is to present a brief introduction to the principles, methods and achievements of quantum cryptography and to discuss its recent advances and the challenges it poses, especially in the area of quantum network security.