This book is based on a study by J. Beemer MSc. providing an introduction and future outlook on renewable energy and cleantech. Using portfolio theory to study the return characteristics of both asset classes. Renewable energy and cleantech, two emerging sectors are analysed extensively for the period 1994 to 2008(ytd) with monthly data and compared with stocks, bonds and alternative asset classes. To study their ability to enhance the performance of an investment portfolio. Both sectors make a valuable contribution to an existing portfolio for investors preferring a portfolio with a higher return than 8.8 percent and who do not mind a standard deviation greater than 4.4 percent. Risk avers investors are better off with a portfolio excluding renewable energy and cleantech, holding only traditional assets. This book makes interesting reading for academics as well as readers with a concern for renewable energy and cleantech.