It is when the American Cancer Society hopes smokers will make a plan to quit, or stop - at least for one day.
This year's theme is "Everyone Loves Quitters."
And now, there are more ways than ever to quit. Seven drugs have government approval.
But while medication is important, adding in counseling dramatically raises the chances for success.
The best way to quit is a combination of medication and counseling.
It is not easy. The average smoker tries quitting 3 to 5 times before he or she stops.
But it is worth the effort.
"Never give up, because it is going to add 10 years to your life, it is going to save you a lot of money, and it is going to allow you to play with your children and grandchildren," says Thomas Glynn.
Here are some of the health effects of quitting:
-Your blood pressure goes down, and you can breathe easier in a little as 12 hours after you stop smoking.
-After 3 months, your risk of 15 different smoking-related cancers drops..
-And at one year, you are half as likely to develop heart disease, and much less likely to go back to smoking.