This chapter discusses how double entry accounting can work in vector spaces. It does so by showing how to present accounting transactions (events) in vector spaces yet according to the double entry principle. The geometric settings used to do so are two- and three-dimensional vector spaces, where a point, line, and space are all a vector or a set of vectors. Accounting events have three intrinsic elements—debit, credit, and size, which were denoted as d, c, and q in previous chapters. Thus, they can be written as a vector. So can accounting events be defined according to the double entry principle. While it is a convention to write vectors as column vectors in linear algebra, all vectors in this chapter are row vectors (for convenience) unless otherwise indicated.