State of the art modeling of investment behavior and analysis of incentive and allocative effects of taxation on investment behavior are reported in these proceedings. Leading researchers from seven OECD countries treat problems ranging from modeling investment behavior and estimating investment equations with various data sets to detailed studies of tax influences on investment behavior. Particular attention is paid to tax reform plans, especially in West Germany and the UK. The role of financial variables and uncertainty is analysed. A major topic in the volume is recent work within Tobin's Q-theoretic framework. Papers report developments and applications of Q-type investment functions, and for the first time estimated Q-theoretic investment equations are presented for West German industries taking into account the complex tax structure.