In everyday life, humans confront situations where different decisions have to be made. Such decisions can be non-trivial even though they often are relatively simple, such as which bus to take or which flavor of a soft drink to buy. When facing decisions of more complex nature, and when more is at stake, they tend to get much harder. It is often possible to deal with such decisions by prioritizing different alternatives to find the most suitable one. In software engineering, decision-makers are often confronted with situations where complex decisions have to be made, and where the concept of prioritization can be utilized. Traditionally in software engineering, discussions about prioritization have focused on the software product. However, when defining or improving software processes, complex decisions also have to be made. In fact, software products and software processes have many characteristics in common which invite thoughts about using prioritization when developing and evolving software processes as well. The results presented in this thesis indicate that it is possible to share results and knowledge regarding prioritization between the two areas. In this thesis, the area of prioritization of software products is investigated in detail and a number of studies where prioritizations are performed in both process and product settings are presented. It is shown that it is possible to use prioritization techniques commonly used in product development also when prioritizing improvement issues in a software company. It is also shown that priorities between stakeholders of a software process sometimes differ, just as they do when developing software products. The thesis also presents an experiment where different prioritization techniques are evaluated with regard to ease of use, time consumption, and accuracy. Finally, an investigation of the suitability of students as subjects when evaluating prioritization techniques is presented.