The thesis consists in three essays. Their common motivation is to provide an explanation for the aftermarket behavior of IPO shares. The first essay is empirical. It deals with the short-term return of IPO shares. Using French data, we show that short-term return for book-built IPO shares is more sensitive to market conditions observed at the time of the offering than when an auction-like mechanism is used. In the second essay, a theoretical model considering the impact of market conditions on the aftermarket price of IPO shares is developed. It allows us to analyze the pricing and allocation of book-built offerings. Hypotheses derived from the model are validated using a sample of recent French offerings. The third essay provides an analysis of three-year stock price performance of IPO shares. First, contrary to previous studies, we do not observe long-term underperformance in our sample. Second, we find that offer prices incorporate correctly the information available at the time of the offering on average. However, some "anomalies" appear.
