Time to celebrate
It's the letter you've been dreaming of; the coveted Notice of Allowance. Only those lucky few ever receive it. After gasping for air and collapsing in a nearby chair, what do you need to do next?

First of all, just make sure there aren't any final corrections to make. Once the patent issues it will become a costly and time consuming matter to correct the spelling of your invention's name in the title, or some other unsightly error. After double checking that everything is in order, all that's left is to send in the issue fee. This issue fee must be paid within 3 months from the date the Notice of Allowance was sent out. There is no chance of extending this time period; it is set in stone. After this fee is paid, it will all be over, the patent will finally be granted.

Hypothetical question
Now just for fun, exactly what happens if the applicant is so busy living it up after receiving the Notice of Allowance that they forget to send in that issue fee? That's not such a big deal is it?  Sorry, but this is definitely a problem.  The PTO will abandon the application if this fee is not paid.

However, in the event this happens it may be possible to revive the application, pay the fee and make things right. The applicant will need to follow the rules for reviving an application in order to make this work. That means they need a legitimate excuse as to why the issue fee was not paid.

Here's another hypothetical situation. After double checking the paperwork, just what if the applicant realizes there is a sizeable mistake in the application? For example, what if he or she finds a publication showing that one of the claims really isn't new at all? This violates the duty to disclose all relevant information to the PTO. That could really cause problems down the road. In this case is there any way to withdraw the application from issue? Fortunately, there is. The applicant may file a petition to withdraw from issue which must include a good reason for withdrawing the application and must also include a fee. Alternately, the Office always reserves the right to withdraw an application from issue if they decide later they made a mistake.