Paternal investment in terrestrial arthropods occurs in three contexts. Prezygotic investment includes indirect contributions to offspring through nutrients provided o the male's mate. Biparental care refers to joint male and female care of offspring. Finally, exclusive paternal care occurs when only the male invests in offspring following oviposition. Examples of exclusive paternal care are known in insects such as assassin bugs (Reduviidae), harvestmen (Opiliones), and millipedes (Diplopoda), although it is far more common in a group of secondarily aquatic insects, namely, the giant water bugs (Belostomatidae). Biparental care is also uncommon and is best developed in burying beetles (Silphidae), dung beetles (Scarabaeidae), and termites (Isoptera). The most pervasive type of paternal investment appears to be prezygotic in the form of spermatophore products and other “nuptial gifts” provided to the female parent. The evolution of paternal investment is a complex process and no single hypothesis nor evolutionary pathway appears adequate to explain the diversity of paternal investment strategies in terrestrial arthropods. As is the case with other animal groups, paternal investment is correlated with certainty of paternity and male territoriality. Ecological factors also appear important, especially in the way these influence the ability of males to enhance the survivorship of offspring and/or the fecundity of their mates. Physically harsh or biotically dangerous habitats and ephemeral, highly prized, productive resources are all associated with high levels of paternal investment. Finally, the indirect sperm transfer strategies common to many terrestrial arthropod species seem to preclude males from contributing materially to their offspring by dissociating parent from progeny. This dissociation may explain in part the relative paucity of high levels of paternal investment by terrestrial arthropods.