This book, as the second volume of a two volume treatise, develops as in the first volume a consistent framework of the investment function that allows for the heterogeneity of capital goods, i.e., the Multiple q model, with theoretical extensions and empirical applications to investment behavior in Japan. Following primary and general analyses developed in the first volume, in this volume (Volume 2) on extensions, the authors extend the Multiple q model to inquire into and statistically test null hypotheses set on rather specific issues such as (a) differences in the adjustment costs by enterprise size and the degree of capital market imperfections, and (b) differences in the adjustment costs by the mode of acquisition such as new purchases, second-hand market acquisitions, and large-scale repairs. The results of the empirical test using Japanese corporate data show that, the investment behavior is heterogeneous not only in terms of the type of capital goods but also in terms of (a) enterprise size and the degree of capital market imperfections, and (b) the modes of acquisition.