When applying for a Mortgage you will have to gather and hand over A LOT of paperwork to your lender. In order to receive a pre-approval or intent to lend, which are the strongest types of letters for sellers to see along with your offer to buy their house. These letters give the seller confidence in your ability to obtain a mortgage loan and differ from a pre-qualification. A good agent will want you to have a pre-approval or intent to lend before presenting your offer to the sellers.

As a former real estate agent I can tell you that when you see the house that you belong in YOU KNOW and you can't wait to sign that offer so it will help to be prepared by already being pre-qualified.
So...what do you need to gather and have prepared for your lender?
First let's start with the rule of 2's.

-Last 2 years W2's/1099's
-Last 2 paystubs showing YTD income or LES
-last 2 months bank statements. Make sure to include ALL pages.

This is all the paperwork to be pre-approved but you will also have to provide your full legal name, date of birth, social security number, and addresses for the past 2 years. If you have been renting the lender may also want to see proof of satisfactory rental history so make sure to have that information available. Keep in mind that this paperwork is the normal necessary paperwork for a pre-approval but could change on a case by case basis...but this will provide a minimum of what will be needed.