: Traditionally, outcomes for patients with relapsed/refractory aggressive B-cell non-Hodgkin lymphoma have been poor. There has been a clear need for effective therapeutic options that could produce durable remissions with a reasonable safety profile. The approval of chimeric antigen receptor (CAR) T-cell therapies has been revolutionary in the field because CAR T-cells meet this need for a substantial number of patients. With multiple approved CAR T-cell products and more expected soon, it can be difficult to distinguish between the various products and decide which to use. Effective CAR T-cell therapeutic choice is enhanced by an understanding of the biology of CAR T-cell, as well as the mechanisms associated with both efficacy and toxicity. : Biology of CAR T-cells, as well as a discussion of their efficacy and toxicity. Mechanisms of resistance, current unanswered questions in the field, issues associated with choosing a CAR T-cell product, and future directions for the advancement of CAR T-cell therapy. : Due to differences in study populations and manufacturing times, it is too early to know if there is a 'best' choice for CAR T-cell therapy. Decisions must be individualized taking into account patient factors and expected toxicity.