Tóm tắt nội dung: This work has been supported by the National Science and Engineering Research Council of Canada, and by the Actuarial Education and Research Fund. I would also like to thank the members of the Department of Statistics at the London School of Economics and Political Science for their hospitality while the book was being completed, especially Anthony Atkinson, Angelos Dassios, Martin Knott, and Ragnar Norberg.