An RRSP is a registered plan that grows on a tax-deferred basis. With an RRSP, the money you contribute is deductible from your income when you file your tax return, which means that you could get some of that money back as a tax refund. Earnings on your investment are also exempt from taxes, as long as you keep them in your RRSP. Withdrawals from your RRSP are included in your regular income and are subject to tax at your marginal tax rate. It can be structured to hold various numerous investments, including mutual funds.