California’s acorn-producing trees, which include eight widespread species of Quercus and a single species of Lithocarpus (the tanbark oak), dominate much of the state and provide key resources for a vast range of wildlife primarily in the form of acorns, production of which varies greatly among individuals, years, species, and populations. Since 1980, we have investigated the causes and consequences of variable acorn production in California oaks in an attempt to understand this phenomenon at both the proximate and ultimate levels. Within populations, we have identified ecological factors that correlate with individual productivity and with environmental factors that correlate with annual productivity. Still unclear, however, is how these environmental factors interact with pollen availability to determine annual variability in acorn production. On a larger geographic scale, our work demonstrates synchronous acorn production within species on a statewide scale. At this level, however, the relative importance of environmental drivers vs. pollen coupling remains to be determined. Finally, California oaks, like those in many other regions, include species that differ in time they require to mature acorns. This ensures that at the community level, masting is unlikely to be extreme and provides strong support for factors beyond predator satiation selecting for masting behavior.