The ancient domain of generation encompassed gods, humans, animals, plants, and some minerals, in hierarchical order. This chapter focuses on the animals and plants, an often overlooked, but vitally important area of both investigation and intervention in classical antiquity. The theoretical framework was most systematically set out by the classical Greek philosopher Aristotle and his pupil Theophrastus, with key aspects vigorously developed in more practical ways by a range of Latin agricultural writers in the Roman period. Generation was an activity shared by all living things (and some inanimate objects), and could, indeed be used to classify and rank these things. It required a male and female principle (though sex was not always necessary); and often involved seed (though plant seed was less seed-like than animal seed). The possibility and process of spontaneous generation was much discussed, as also themes of animal hybridity and plant grafting, along with more general matters of livestock breeding and crop production; all emphasizing the fluid continuity, and fecundity, of ancient notions of nature.