This paper presents a review of lightning return-stroke models based on transmission line theory. The reviewed models are classified in three different categories, namely discharge-type, lumped-excitation, and parameter-estimation models. An attempt is made to address the difficulties that some models experience in reproducing directly or indirectly observable features of lightning, such as current characteristics and remote electromagnetic fields. It is argued that most of these difficulties are related to a poor discretization of the lightning channel, to inconsistencies in the calculation of per-unit-length channel parameters, to uncertainties in the representation of the upper end of the channel, and to assuming an ideal switch to connect the channel to ground in the transition from leader to return stroke. Applications of transmission line return-stroke models are also outlined.