A Roth IRA is an individual retirement account (IRA) under United States law that is generally not taxed upon distribution, provided certain conditions are met. The principal difference between Roth IRAs and most other tax-advantaged retirement plans is that rather than granting an income tax reduction for contributions to the retirement plan, qualified withdrawals from the Roth IRA plan are tax-free, and growth in the account is tax-free.

The Roth IRA was introduced as part of the Taxpayer Relief Act of 1997 and is named for Senator William Roth.

A Roth IRA can be an individual retirement account containing investments in securities, usually common stocks and bonds, often through mutual funds (although other investments, including derivatives, notes, certificates of deposit, and real estate are possible). A Roth IRA can also be an individual retirement annuity, which is an annuity contract or an endowment contract purchased from a life insurance company. As with all IRAs, the Internal Revenue Service mandates specific eligibility and filing status requirements. A Roth IRA's main advantages are its tax structure and the additional flexibility that this tax structure provides. Also, there are fewer restrictions on the investments that can be made in the plan than many other tax-advantaged plans, and this adds somewhat to their popularity, though the investment options available depend on the trustee (or the place where the plan is established).

The total contributions allowed per year to all IRAs is the lesser of one's taxable compensation (which is not the same as adjusted gross income) and the limit amounts as seen below (this total may be split up between any number of traditional and Roth IRAs. In the case of a married couple, each spouse may contribute the amount listed):

Originally called an "IRA Plus", the idea was proposed by Senator Bob Packwood of Oregon and Senator William Roth of Delaware in 1989. The Packwood–Roth plan would have allowed individuals to invest up to $2,000 in an account with no immediate tax deductions, and the earnings could later be withdrawn tax-free at retirement.

The Roth IRA was established by the Taxpayer Relief Act of 1997 (Public Law 105-34) and named for Senator Roth, its chief legislative sponsor. In 2000, 46.3 million taxpayers held IRA accounts worth a total of $2.6 trillion in value according to the Internal Revenue Service (IRS). Only a little over $77 billion of that amount was held in Roth IRAs. By 2007, the number of IRA owners had jumped to over 50 million taxpayers with $3.3 trillion invested.

In 1997, Roth wanted to restore the traditional IRA which had been repealed in 1986, and the upfront tax deduction that goes with it. Under congressional budget rules, which worked within a 10-year window, the revenue cost of giving that tax break to everyone was too high, so his staff limited deductible IRAs to people with very low income, and made Roth IRAs (initially with income limitations) available to others. This slid the revenue cost outside the 10-year window and got the legislation out from under the budget rules.

Economists have warned about exploding future revenue losses associated with Roth IRAs. With these accounts, the government is "bringing in more now, but giving up much more in the future," said economist and Forbes contributor Leonard Burman. In a study for The Tax Policy Center, Burman calculated that from 2014 to 2046, the Treasury would lose a total of $14 billion as a result of IRA-related provisions in the 2006 tax law. The losses stem from both Roth conversions and the ability to make nondeductible IRA contributions and then immediately convert them to Roths.