There's sort of 3 usually... the initial one is a prequalification. That means as long as you can prove everything you claimed, you will be approved. The you submit documents for preapproval. If that goes through ok and you were able to verify everything you claimed about income, debts, and credit scores you can start shopping for homes. Then it goes to underwriting and they do tend to ask for more documentation and more current documentation (ie. they'll pretty much keep asking for updated bank statements right until closing) throughout the process until closing. It seems as if you're constantly having to provide more and more documents even after you put in an offer, have it accepted, and are "set to close" 
