The fly family Tabanidae (horse flies) includes an estimated 4500 extant species distributed throughout the world. Nearly all are blood-feeders as adults, but many are also important pollinators of angiosperm  flowers. The biology and taxonomy of horse flies has an important historical legacy, but modern phylogenetics-based revisionary work has lagged behind other dipteran groups due to a generational reduction in the number of horse fly taxonomists and to a perceived "difficult" morphology which is often homogeneous for many standard dipteran characters (e.g., male genitalia) and/or highly adapted in others (floral-associated features). Current classifications are heavily biased by several large traditional genera, while many smaller groups need to be addressed to provide context and new characters from which more comprehensive phylogenetic revision can proceed.