Digital communication is penetrating into more and more areas of private and business applications. The legal framework for legally secure processes on the Internet was created in Germany in 1997. The central component is the digital signature. The authors explain its concept and possible applications clearly and in detail. The functions of signature, trust center, smart card, and asymmetric key procedure are presented and illustrated by numerous diagrams. The information serves as a basis for decisions on the use of the digital signature in companies, institutions, and authorities. The application examples refer to business-to-business and business-to-customer relationships in intranets and the Internet. The work is primarily aimed at producers of digital media and decision-makers in business and administration.