Fornication, wrote Fathers Magin Catala and Jose Viader in 1814, ranked among most dominant vices of the at Mission Santa Clara, near the San Francisco Bay in Alta California.1 Other missionaries agreed. dominant vices of the wrote Fathers Narciso Duran and Buenaventura Fortuny from nearby Mission San Jose, those which are prohibited in the fifth, sixth, seventh and the first part of the eighth commandments of the holy law of God.2 Those commandments enjoined believers to refrain from murder, fornication, theft, and lying. Of the sixteen missions responded to the question, Which vices are the most dominant among them and in which sex?, thirteen mentioned impurity, unchastity, incontinence, lust, or fornication.3 Clearly, to the missionaries, sexual immorality was a major problem. But how did the Central Californians themselves perceive their sexual conduct? By reinterpreting the missionaries' reports about Native Americans' marriage and sexuality in Missions San Francisco, Santa Clara, and San Jose in the light of anthropological evidence on Central Californian Indians, I argue what the missionaries saw as the sexual immorality of Catholic Indians, the Central Californians themselves likely interpreted as legitimate sexual behavior. Before the Spanish arrived, many small tribelets occupied the San Francisco Bay area. They spoke dialects of five mutually unintelligible languages: Costanoan, Bay Miwok, Coast Miwok, Patwin, and Wappo. Anthropologists and historians believe these tribelets were culturally similar, though geography and ecology caused some differences between tribelets in different areas. Tribelets interacted regularly, creating social, political, and economic ties bound them to their neighbors.4 For the Spanish crown, the Alta California missions were an inexpensive means of establishing a physical presence in lands claimed by the Spanish crown, thus discouraging incursions by the British, Americans, and Russians. Missions San Francisco, Santa Clara, and San Jose were among the last of the missions to be founded, beginning in 1776, 1777, and 1797, respectively. As they founded missions, the Spanish also established military outposts and civil settlements, the latter often inhabited by soldiers and, occasionally, their families. Men formed the overwhelming majority of the early settlers in Alta California. The first president of the California missions, Junipero Serra, urged the government to send more families to live in the region, so that the Indians, who until now have been very surprised to see all the men without any women, see there are also marriages among Christians.5 In the San Francisco Bay area, the Hispanic colonists built the San Francisco presidio in 1776 and settled the town of San Jose in 1777. Fourteen families lived in San Jose, nine of them headed by soldiers.6 The settlements grew slowly; by 1810, according to the historian of California Hubert Howe Bancroft, the Hispanic population of the Bay Area remained under five hundred.7 Scholars studying the Spanish missions in Aha California disagree-sometimes vehemently-about whether the mission system was helpful or harmful to the Native American population of the area. Yet whether they see the missions as an oppressive regime designed to destroy Native American cultures or as the most effective means of protecting Indians from the deleterious effects of Spanish invasion, scholars rarely question the ideological dominance of Catholicism within the mission walls. Scholars who see the mission system in a positive light tend to follow the missionaries' own understanding of the missions as islands of Catholicism in a sea of traditional Indian religion.8 On the other side of the debate, scholars who see the missions as oppressive institutions have tended to be interested in Native American resistance to the mission system. They have focused their research on physical resistance, primarily in the forms of armed conflict and fugitivism. …