Linear algebra is the branch of mathematics that, among other things, studies vectors and matrices. Vectors are mathematical elements essential to understanding the spatial relationships between points, lines, and planes. In addition, they are essential to understand electromagnetism, which is one of the theoretical pillars of electroencephalography (and neurophysiology in general). In this chapter, we will review the concepts of canonical basis and the main operations with vectors, such as addition and scalar and vector products. We will also briefly see other coordinate systems, in addition to the Cartesian, such as the cylindrical and spherical. Finally, as part of a more advanced treatment of the subject, the concepts of gradient, divergence, curl, and Laplacian will be shown, which are of great importance in electromagnetism.