Preferences and utility theory are critical concepts in microeconomics, explaining household decision-making behavior. Preferences refer to how households make choices necessary to satisfy their needs when comparing bundles of goods. Utility theory uses mathematical concepts to express these preferences and elucidate household satisfaction levels. Rational preferences must meet completeness, transitiveness, continuity, convexity, and monotonousness. Various preferences exist, including substitutes, complements, perfect and imperfect substitutes, and perfect compliments. Preference and utility theory ultimately help derive the formal opportunity costs of alternatives in household theory.