Year-to-year changes in the state’s higher education costs are greatly influenced by changes in student enrollment levels. Each year as part of the annual budget process, the Legislature must determine (1) how many additional students will enroll at the University of California and the California State University and (2) how much it will cost to serve those additional students. This report reviews factors that influence enrollment growth and the current methodology of calculating the “marginal cost” of serving additional students. Specifically, for 2006-07, we recommend, first, funding 2 percent enrollment growth at UC and CSU and second, revising the current methodology for calculating the marginal cost of enrolling an additional student, in order to more accurately budget for these expenses.