Advanced Textbooks in Economics: Investment: The Study of an Economic Aggregate focuses on the principles, methodologies, and approaches involved in the determination of investments. The book first offers information on the theories of aggregate investment and statistical and questionnaire studies. Discussions focus on statistical studies, tax incentives and disincentives to investment, capital stock adjustment models, acceleration principle, replacement investment, level of aggregation, sources of funds, neoclassical theory of capital accumulation, and tax incentives and disincentives to investment. The text then examines the estimation of lag distributions, including geometrically declining lag distributions, Pascal and rational distributions, variable lag distributions, and the first-in first-out method. The publication ponders on econometric studies, as well as United Kingdom and United States studies, two-stage studies of investment, and guidelines for future research. The text is a dependable source of information for economists and researchers interested in economic aggregates.