Compulsive behavior (or compulsion) is defined as performing an action persistently and repetitively. Compulsive behaviors could be an attempt to make obsessions go away. Compulsive behaviors are a need to reduce apprehension caused by internal feelings a person wants to abstain from or control. A major cause of compulsive behavior is obsessive–compulsive disorder (OCD). "Compulsive behavior is when someone keeps doing the same action because they feel like they have to, even though they know these actions do not align with their goals." An individual may perform certain actions in an attempt to prevent or reduce anxiety, uncertainty, or negative consequences. The elements that make a behavior compulsive is when one feels the need to do an action, cannot stop themselves from doing that action, and being aware that these actions go against their goals. These actions are done in a habitual and repetitive manner with a specific pattern.

There are many different types of compulsive behaviors including shopping, hoarding, eating, gambling, trichotillomania and picking skin, itching, checking, counting, washing, sex, and more. Also, there are cultural examples of compulsive behavior.

Addiction and obsessive–compulsive disorder (OCD) feature compulsive behavior as core features. Addiction is simply a compulsion toward a rewarding stimulus, whereas in OCD, compulsions are an attempt to reduce distressing and obsessive thoughts. The compulsive behaviors that individuals with OCD do are often related to their obsessive thoughts. The most common compulsions for people with OCD are washing and checking.

Addiction is not a compulsive behavior in the beginning stages. An individual typically derives pleasure from the substance or behavior in the beginning. After some time, the addiction can become a compulsive behavior when that individual begins to depend on the substance or behavior for relief rather than pleasure.  Many people with OCD also suffer with substance abuse disorder.

While not all compulsive behaviors are addictions, some such as compulsive sexual behavior have been identified as behavioral addictions.

About 50 million people in the world today appear to have some type of obsessive–compulsive disorder. Affected people are often more secretive than other people with psychological problems, so the more serious psychological disorders are diagnosed more often. Many who exhibit compulsive behavior will claim it is not a problem and may endure the condition for years before seeking help.

Compulsive shopping is characterized by excessive shopping that causes impairment in a person's life such as financial issues or not being able to commit to a family. The prevalence rate for this compulsive behavior is 5.8% worldwide, and a majority of the people who are affected by this type of behavior are women (approximately 80%). There is no proven treatment for this type of compulsive behavior.

Hoarding is characterized by excessive saving of possessions and having problems when throwing these belongings away. Major features of hoarding include not being able to use the capacity of one's living quarters efficiently, having difficulty moving throughout the home due to the massive amount of possessions, as well as having blocked exits that can pose a danger to the hoarder and their family and guests. Items that are typically saved by hoarders include clothes, newspapers, containers, junk mail, books, craft items, bills and receipts, and household supplies. Hoarders believe these items will be useful in the future or they are too sentimental to throw them away. Other reasons include fear of losing important documents and information and object characteristics. Hoarding can be harmful if it poses a health risk to the person and/or others in their house. Examples of health risks include clutter creating unhygienic conditions encouraging potential rodent or insect infestations, fire risks, or trip and fall risks.