This study summarizes the existing information on the Roman domestic cult and illustrates it by a study of the archeological evidence. The household shrines (lararia) of Pompeii are discussed in detail. Lararia from other parts of the Roman world are also studied. The domestic worship of the Lares, Vesta, and the Penates, is discussed and their evolution is described. The Lares, protective spirits of the household, were originally rural deities. However, the word Lares was used in many different connotations apart from domestic religion. Vesta was closely associated with the family hearth and was an ancient agrarian deity. The Penates, whose origins are largely unknown, were probably the guardian spirits of the household storeroom. All of the above elements of Roman domestic worship are present in the lararia of Pompeii. The Genius was the living force of a man and was an important element in domestic religion. The Genius of the paterfamilias, head of the Roman family, was worshipped in the home along with the other domestic deities. The Greek Agathos Daimon was similar to the Genius in certain respects, but the exact relationship between the two is not clear. One religious symbol shared by both is the serpent. The history of the serpent in Greek and Roman religion is described in detail. The Genius and the serpent are both common religious subjects in the lararia of Pompeii. The archeological evidence includes the lararia, domestic altars, and wall paintings found at Pompeii. The lararia are interpreted and their role in the domestic cult is described; they are also illustrated by twelve plates. Lararia have also been discovered in Herculaneum, Ostia, Delos, Spain, and Africa. The abundant archeological evidence found in the Roman world demonstrates the importance of Roman domestic worship in Roman life.