Current population projections indicate that California could add more than 10 million new residents over the next 20 years. Yet the population projections themselves are the subject of some uncertainty. This report seeks to inform the state’s population projections by offering a fine-grained analysis of the state’s fertility trends. It focuses on two questions: how much does fertility vary by immigrant generation in California, and what are the relationships between personal characteristics, neighborhood characteristics, and fertility rates among the state’s immigrant population and their descendants? The report concludes that immigrant generation is not independently important once personal characteristics are controlled for, but that the predictive value of this factor is still useful for projecting fertility changes. It also suggests that current population projections for California may be too high because they do not consider declines in fertility as immigrants and their descendants adapt to life in this country.