I am 57 and my wife is 54. We both have traditional IRAs which, at this point, is just sitting in cash. I have been contemplating whether it would be beneficial tax wise to convert the IRAs to Roths.

This question pertains not so much to whether going the Roth route is a good or bad idea, although I welcome such comments. My question at this point is whether IF one converts a traditional IRA to a Roth, is it an all-or-nothing transaction? For example, is it possible to do a partial conversion so that one can strategically convert amounts annually so as to minimize the tax hit over a period of years? Or, do the conversion rules require that the entire IRA be converted at one time?