There are five castes in the novel. In descending order, they are named for the first five letters of the Greek alphabet, Alphas, Betas, Gammas, Deltas, and Epsilons. The upper castes are bred to be the intelligent part of society in positions of management. The lower castes are bred to do the menial tasks of society. Each caste is conditioned during their sleep to be happy with their caste and not want to be a part of any other caste.