The purpose of this dissertation is to develop a theory that helps explain the conditions under which firms select certain project evaluation techniques. This study uses contingency theory to analyze the impact of environmental uncertainty on the choice of project evaluation techniques. In addition to a direct measure of uncertainty, several dimensions of uncertainty are included in this study. These dimensions of uncertainty include control structure, method of financing, foreign assets, method of growth, and product domination. This study also analyzes the use of project evaluation, management science and risk management techniques in US firms over time and in UK firms over time in order to compare to prior research. A comparison of firms in the two countries are also provided. The primary method of data collection was a survey instrument. Data were also collected from annual reports and various other public sources. The variables that appear significant in the choice of project evaluation technique in US firms are environmental uncertainty, control structure, method of financing, foreign assets, and product domination. The variable that appear significant in the choice of project evaluation technique in UK firms is method of financing. US firms favor discounted cash flow techniques although this study detected a slight decrease over time. UK firms continue to use non-discounted cash flow techniques, although the use of discounted cash flow techniques is widespread. There are significant differences between US and UK firms. US firms tend to use discounted cash flow techniques to a greater extent than UK firms. This research makes a significant contribution in attempting to develop a theory explaining the use of project evaluation techniques in firms in the US and UK. In addition, several other developments relating to project evaluation, management science and risk management are discussed. The results of this study can be used by managers in refining and improving their existing project evaluation processes.