In this paper the most important aspects for designing dynamic barriers for protection against rockfalls are presented. Technological advances in fabrication of metallic materials are increasingly enabling the use of barriers with greater ability to absorb energy. However, in order to establish what type of barrier is needed to solve a given problem ( location, height and energy), it is necessary to know the basic principles of the way these elements function, as well as the design methodology to be applied. In the following paragraphs of the paper the basic concepts that should be taken into account by the engineer responsible for the design of a barrier are described, and, by applying a commercial software, a real example of the design of a rockfall protection system on a hillside is finally illustrated.