In Pair Programming (PP), two programmers are working together side by side on the same task, using a single computer. The benefits are well documented in experimental studies and include improved design quality, reduced defects, reduced staffing risks, enhanced technical skills, and improved team communication. However, the success of PP highly depends on how the pairs match. Based on the hypothesis that the partners' personality influences pair compatibility and code quality, this book describes an empirical study that investigates which personality traits are crucial for PP. First, programmers with industry experience were surveyed in order to identify the most important personality traits for PP. Second, computer science students were matched based on their personality and given a series of assignments. Third, the PP-success was evaluated by measuring the pairs' compatibility and the quality of the code produced. For managers in the software industry, this book offers an approach to improve the outcome of PP by optimizing the compatibility of programming partners. For researchers, it presents a bases for further analyses on significant factors to improve the efficiency of PP.