If you have received this notice, it means you have failed to file a tax return. The type of return and tax period will be shown in the upper right corner as well as in the body of the notice. You received this notice because the IRS has reason to think you meet the filing requirements and they have not received a return. File your return as soon as possible or you will need to explain to the IRS why you don't need to file.
Sections of the Notice:
Sample CP 59: PDF Pages 1-4
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.