From a practical standpoint, the process of accounting consists of four sequential activities: measuring, recording, aggregating (summarizing), and reporting. The most important among these activities is the second step recording—the recording of accounting transactions (events) according to the double entry principle. This step is at the heart of accounting and makes double entry accounting so unique. It was for this reason why all previous chapters focused on the recording step of the accounting process, namely the presentation of accounting events in geometric and vector spaces according to the double entry principle. This chapter examines the next step aggregating of the accounting process. It discusses how to aggregate monetary measures in accounting in geometric and vector spaces yet according to the double entry principle. The geometric setting used to do so is a two-dimensional debit-credit Cartesian space. A three- or higher-dimensional geometric setting is not relevant since the aggregations of monetary measures at different levels in accounting take place with respect to the debits and credits of individual accounts and groups of accounts.