Customer satisfaction with regard to user interfaces becomes increasingly more important and is, eventually, decisive for the selection of systems within a competitive market. End-users demand benefits and a clear increase in value. They expect efficient and optimum support in their work with their interfaces. One possible method to achieve this is User- Centered Design, which means to incorporate end-users in the interface development from scratch. Essential is the knowledge about the end-user, which in return, will lead to better insights into their thinking and behavior, consequently resulting in better user interfaces. The challenge is to combine complex back-end functionalities with a well operated, attractive, effective and efficient user interface. Thinking Aloud (THA) is one of the most valuable usability engineering methods to address this challenge. In combination with the use of paper mock-ups and appropriate tasks software engineers are able to gain insight into the thinking and behaviour of their end users. Videos taken during the THA sessions can be analyzed and the insights integrated into redesign. THA was first used by psychologists during research in problem solving.