The Date Format in the Import Options window is where you tell CheckBook the format that’s in the file you’re importing, so you’ll want to choose YYYY/MM/DD. The format that’s displayed in your Entries is according to the format your Mac is set to use, though you get to choose between the Mac's short (probably MM/DD/YYYY) or long date format in CheckBook’s preferences. I’d go ahead and set the Date Format in Import Options to YYYY/MM/DD now, then check out how things look in your Entries. The default will probably be just what you’re expecting - but if you need a hand from there, let us know!