Form 540 is the standard income tax form that all California residents use, as the California Franchise Tax Board explains. Form 540 has various variants, including 540EZ and 540NR, which comes in short and long versions.
A taxpayer must use Form 540 if he has income from any sources other than wages noted on a W-2 form or income noted on a 1099 form. Form 540 is also necessary to claim any deductions other than the standard deduction or any credits other than the renter's credit. In addition, anyone claiming more than three exemptions or any exemptions other than the personal or senior exemption must use Form 540. Form 540EZ is a simplified version of Form 540 for people with simple tax returns. Non-residents of the state use Form 540NR, according to the Franchise Tax Board.