Form I-9, Employment Eligibility Verification is used for verifying the identity and employment authorization of individuals hired for employment in the United States. All U.S. employers must ensure proper completion of Form I-9 for each individual they hire for employment in the United States. This includes citizens and noncitizens. Both employees and employers (or authorized representatives of the employer) must complete the form.

IRS W4 Calculator:

Use this handy calculator to help figure out what you should be claiming on your Form W4.