The four papers that make up my thesis take different approaches to portfolio choice. The first paper, Expertise Bias, is an empirical paper investigating individuals' portfolio choice. The main finding is that individual investors have an excess weight (according to standard portfolio theory) in stocks related to their expertise. The investigation of this research question is possible due to a unique Norwegian data set that follows all Norwegian citizens. For each individual, the data set contains information that can connect his expertise (e.g. history of employment, experience, education, and wage) with his stock holding (all individual stocks). In addition, the data set includes many socioeconomic and portfolio variables. The next two ...