Abstract: Relative categories are maybe the most naive model for abstract homotopy theory (just categories with a subcategory of "weak equivalences"). Barwick and Kan showed that the category of relative categories has a model structure, Quillen equivalent to the Joyal model structure on simplicial set, which has infinity-categories as fibrant objects. We will show that model categories define fibrant relative categories and also discuss other aspects of the homotopy theory of relative categories.