Converting pre-tax dollars to a Roth IRA essentially counts as income. For example, if you have a Traditional IRA or a 401k, those are funded with pre-tax dollars. When you convert to a Roth, that becomes income which you must pay taxes on. The advantage is that since you just paid taxes on those funds, all future withdrawls are now tax-free. This can be a great technique if you have no income in a given year and can take advantage of low tax rates.