Motivic homotopy theory, as introduced by Fabien Morel and Vladimir Voevodsky, constitutes a homotopy theory for smooth varieties over a field, in which the affine line plays the role of the interval parameterizing homotopies. This talk will introduce the subject, with an emphasis on the similarities with classical homotopy theory, on applications to the study of vector bundles, and on computations of homotopy groups.