Cravings (the urge or desire to smoke) can be due to nicotine withdrawal. However, they can also be triggered by things that you've learned to link with smoking.
Triggers, can be quite varied. For example, they can be linked to places where you normally smoked, people who you usually smoked with, and being near other people smoking. Similarly, habits or routines such as smoking after meals, drinking coffee or alcohol, or talking on the telephone may bring on cravings.
A lot of people feel the urge to smoke when they feel angry, bored, tense or happy; or when they want to relax. Often, it's a combination of place, activity and emotions that create a strong urge to smoke.
Some people have occasional urges to smoke long after other withdrawal symptoms have gone. If this happens to you, try not to be disheartened. Explore the Staying Quit section of this website. Even though you've decided that you want to be a nonsmoker, there may be times when you still have a desire to smoke. Remind yourself why you want to quit and think how far you've come and what you've gained. As you become used to doing other things instead of smoking in situations which trigger cravings, these urges to smoke tend not to happen as often and be less strong.