The mos maiorum (lit. ways of the ancestors) were the ancestral traditions, an unwritten code of laws and conduct, of the ancient Romans. It institutionalized cultural traditions, societal mores, and general policies, as distinct from specific laws.

The eight cornerstones of mos maiorum were:

• fides — fidelity, loyalty, faith
• pietas — piety, devotion, patriotism, duty
• religio — religious scruple, reverence for higher power(s), strictness of observance, conscientiousness precision of conduct
• disciplina — discipline, diligence
• constantia — firmness, steadiness
• gravitas — seriousness, dignity, authority
• parsimonia — frugality
• severitas — strictness in the moral sense

It was partially typified by a respect for fathers and husbands and acknowledgement of one's subservience to them. One of the best illustrations of this tradition is found in the writings of Cato the Elder.