A certified public accountant (CPA) has usually studied accounting at a college or university and passed a standardized CPA exam. He or she has a certain number of years of public accounting experience as required by the state's licensing board.
Enrolled agents (EAs) are licensed by the IRS and specifically trained in federal tax planning. They've either passed a comprehensive exam or worked at the IRS for at least five years in some capacity in which they're interpreting or applying the tax code.
Other tax professionals may have taken continuing education courses in accounting. The IRS recommends paid tax return preparers participate in a voluntary program that offers training in basic tax filing, ethics and federal tax law. (The IRS had required mandatory testing of paid tax return preparers, but those regulations were struck down by a federal appeals court last year.)
Some attorneys also specialize in tax preparation and planning. Attorneys should have earned a law degree and passed a bar exam and should be licensed by their state or the District of Columbia. The IRS provides a searchable database of tax return preparers who hold professional credentials it recognizes – including CPAs, EAs, and attorneys -- on its website.