The February 2009 state budget agreement changed the apportionment formula used to determine California taxable income for firms that also operate in other states. While the current formula considers the location of firms’ sales, property, and payroll, starting in 2011 firms will have the option to consider only their sales. This policy is intended to encourage firms to produce in California and sell into other states. In this report, we examine the rationales for different approaches to apportionment and evidence from California and other states on how changes to apportionment laws affect both economic activity and tax revenue. Our findings indicate that: (1) a formula with a higher weight on sales and lower weights on property and payroll promotes job growth to some extent; (2) with most states’ formulas now based only on sales, the old formula that used property and payroll could put some California producers at a competitive disadvantage; and (3) allowing firms to choose their formula every year arbitrarily favors some firms over others. We recommend that the state require all firms to use the single sales factor, which would help the state’s competitiveness while limiting the cost to the budget.