This dissertation is composed of four chapters that make a substantial contribution to existing knowledge of the trading behavior and performance of individual investors. The first chapter provides the most extensive study of the trading performance of French individual investors to date. Based on a large database of nearly 8 million trades realized by56,723 investors, we show that French investors exhibit negative risk-adjusted returns on their portfolios, and make penalizing choices in their trades. We find that more sophisticated investors do not perform better than their peers, and we conclude that investors would gain more from applying a passive strategy. In the second chapter, we evidence that individual aspiration is a key determinant of existing heterogeneity in portfolio performance. We define aspirations according to the Behavioral Portfolio Theory. Investors who have high aspirations hold riskier portfolios, trade more frequently and diversify less than investors who have low aspirations. After controlling for turnover, diversification and usual risk factors, we find that investors with high aspirations underperform investors with low aspirations.In the third chapter we highlight alternative measures of performance that efficiently convey the real preferences of investors. When they are evaluated with these alternative measures rather than with the Sharpe ratio, a higher proportion of investors beat the market index. This observation challenges the global evidence that individual investors are poor portfolio managers. However, our evidence suggests that the improvement of an investor’s performance is linked to portfolio skewness rather than relevant stock selection.In the last chapter, we explore the repurchase behavior of individual investors. We find that French investors prefer to repurchase (1) stocks that have been sold for a gain and (2) stocks that have lost value since their sale. Our tests exclude rational explanations for these preferences and confirm our hypothesis that such patterns can be traced to the avoidance of regret in trades. We use survival analysis to demonstrate that sophisticated investors suffer less from there purchase preferences.