Smoking cessation, usually called quitting smoking or stopping smoking, is the process of discontinuing tobacco smoking. Tobacco smoke contains nicotine, which is addictive and can cause dependence. As a result, nicotine withdrawal often makes the process of quitting difficult.

Smoking is the leading cause of preventable death and a global public health concern. Tobacco use leads most commonly to diseases affecting the heart and lungs, with smoking being a major risk factor for heart attacks, strokes, chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), emphysema, and various types and subtypes of cancers (particularly lung cancer, cancers of the oropharynx, larynx, and mouth, esophageal and pancreatic cancer). Smoking cessation significantly reduces the risk of dying from smoking-related diseases.

From 2001 to 2010, about 70% of smokers in the United States expressed a desire to quit smoking, and 50% reported having made an attempt to do so in the past year. Many strategies can be used for smoking cessation, including abruptly quitting without assistance ("cold turkey"), cutting down then quitting, behavioral counseling, and medications such as bupropion, cytisine, nicotine replacement therapy, or varenicline. In recent years, especially in Canada and the United Kingdom, many smokers have switched to use electronic cigarettes in order to quit smoking tobacco.

Most smokers who try to quit do so without assistance. However, only 3–6% of quit attempts without assistance are successful long-term. Behavioral counseling and medications each increase the rate of successfully quitting smoking, and a combination of behavioral counseling with a medication such as bupropion is more effective than either intervention alone. A meta-analysis from 2018, conducted on 61 randomized controlled trials, showed that among people who quit smoking with a cessation medication (and some behavioral help), approximately 20% were still nonsmokers a year later, as compared to 12% who did not take medication.

In nicotine-dependent smokers, quitting smoking can lead to symptoms of nicotine withdrawal such as nicotine cravings, anxiety, irritability, depression, and weight gain.^: 2298 Professional smoking cessation support methods generally attempt to address nicotine withdrawal symptoms to help the person break free of nicotine addiction.