Task analysis and cognitive task analysis are terms that should be put in focus in modern systems development. These terms contains numbers of techniques and methods which all share the same goal of describing what happens in a situation but also during later years, trying to explain why something happens. This report describes differences between traditional task analysis and cognitive task analysis, and provides a deeper presentation of the cognitive task analysis method "Critical Decision Method" (CDM). Two cases where the CDM has been used are described. In the first case the goal was to identify cognitive skills with the purpose of developing tests to use for selection of Swedish combat-boat drivers in the amphibious corps. In the latter case the goal was to investigate and give suggestions how the interface should be designed for a warning and countermeasure system in combat vehicle 90. The method served the purpose well and is a great tool for making mental processes and behavior explicit. The method might need to be modified from case to case.