Tensors are introduced as a generalization of vectors and vector fields. As in the rest of the book, the discussion in this chapter is limited to a flat (Euclidean) three-dimensional, simply-connected Cartesian space. Tests for tensor character are demonstrated, and tensor operations are briefly discussed. The metric is then added to give meaning to the concept of distance in the space. The chapter concludes by touching lightly on the idea of invariance. In-chapter examples and end-of-chapter problems are included to reinforce introduced concepts and to give readers a chance to practice the relevant mathematics.