Essay from the year 2002 in the subject Business economics - Banking, Stock Exchanges, Insurance, Accounting, grade: 1,9 (B+), Oxford Brookes University (Business School), course: International Finance & Investment, language: English, abstract: Ever since in the history of stock markets, financial theorists try to understand how investors take decisions under uncertainty in order to value stocks precisely and predict their future returns. Their wish to develop a consistent model gave raise for various theoretical approaches and empirical examinations. This work tries to give a short overview on the traditional theory of asset pricing and discusses the need for a paradigm change due to the recent development in the US and UK stock markets.