Do I apply for loans before or after finding the property I want?

[Jeff L.]

Do I visit the bank to get funding before or after finding the property I want to buy?

I'm starting out and have no idea when I'll find the property I'm going to put an offer on. Should I go to the bank now and start the process now?

It seems strange to go mortgage shopping before I know when I'll be making the purchase. Is there a length of time before the "preapproval" expires?