Consumer behavior and equilibrium can be analyzed using utility theory and indifference curves. Utility refers to the satisfaction received from consuming goods, with marginal utility declining as consumption increases per the law of diminishing marginal utility. Indifference curves graph combinations of goods that provide equal utility. The budget line shows affordable combinations given prices and income. Consumer equilibrium occurs where the marginal rate of substitution between goods equals the price ratio, and is at the highest indifference curve possible given the budget.