What are the primary differences between the different 1040 forms?

Two of the forms used for filing individual federal income tax returns are IRS Form 1040A and IRS Form 1040EZ. Trhe third one is the complex IRS Form 1040. Form 1040EZ is the briefest version of the 1040. You can't itemize deductions or claim any adjustments to income or tax credits except for the Earned Income Credit, and you can't have any income from self-employment, alimony, dividends or capital gains.