The prevalence of unmet need for family planning is a primary justification for family planning programs, but the causes of unmet need have not been much explored. This article investigates four explanations for unmet need: (1) as an artifact of inaccurate measurement of fertility preferences and contraceptive practice; (2) as a reflection of weakly held fertility preferences; (3) as a result of women's perceiving themselves to be at low risk of conceiving; (4) as due to excessive costs of contraception. The explanations are examined using quantitative and qualitative data collected in 1993 from currently married women and their husbands in two provinces in the Philippines. The results indicate that the preference-behavior discrepancy commonly termed "unmet need" is not an artifact of survey measurement. The most important factors accounting for this discrepancy are the strength of women's reproductive preferences, husbands' fertility preferences, and the perceived detrimental side effects of contraception. Inaccessible family planning services appear to carry little weight in this setting. Modification of services to make them more attentive to other obstacles to contraceptive use would improve their effectiveness in reducing unmet need.