This paper aims to introduce programming using Design by Contract (DbC) approach, its principles and implementations in different environments. The motivation for the creation of this approach is discussed in the beginning and the DbC metaphor is explained, as well as its application to programming. The description of major elements of the contract in the context of routine interface follows afterwards. The subject matter of this paper is the analysis and comparison of individual programming systems for DbC development with the help of code samples. The benefits of using this approach and its role in the modern development process are evaluated in conclusion.