The book surveys modern literature on financial aggregation and index number theory, with special emphasis on the contributions of the book's two coauthors. In addition to an introduction and a systematic survey chapter unifying the rest of the book, this publication contains reprints of six published articles central to the survey chapter. Financial Aggregation and Index Number Theory provides a reference work for financial data researchers and users of central bank data, placing emphasis on possible improvements in such data from use of the microeconomic index number and aggregation theory.