Fetishism is a fixation on an inanimate object or body part that is not primarily sexual in nature, and the compulsive need for its use in order to obtain sexual gratification. It is almost exclusively a male paraphilia. The object of a fetish is almost invariably used during masturbation and may also be incorporated into sexual activity with a partner in order to produce sexual excitation. Inanimate object fetishes can be categorized into two types: form fetishes and media fetishes. In a form fetish, it is the object and its shape that are important, such as in the case of high-heeled shoes. In a media fetish, it is the material out of which the object is made that is important, such as silk or leather. Inanimate object fetishists often collect the object of their favor, and may go to great lengths, including theft, to acquire just the "right" addition for their collection.
Although the list of objects that fetishists can use for sexual gratification is inexhaustible, among the more common inanimate objects are panties, bras, slips, stockings or panty hose, negligees, shoes, boots and gloves. Common media objects include leather, rubber, silk, or fur. In some cases drawings or photographs of the fetish object may arouse fetishists, but more commonly the fetishist prefers or requires an object that has already been worn. The worn object does not serve as a symbolic reminder of the former owner, however, because it is the object that the fetishist relates to, not the person attached to it. Sometimes it is a body part, such as hair, feet, legs or buttocks that become fetish objects. These are examples of animate fetish objects.

The sexual acts of fetishists are characteristically depersonalized and objectified, even when they involve a partner. The focus of attention is exclusively on the fetish, whereas non-fetishists may at various times make a particular body part or an object part of their general sexual arousal and expression with another person, but not be fixated on it.

In some cases, the fetishist can become sexually aroused and orgasmic only when the fetish is being used. In other instances, a sexual response may occur without the fetish, but usually at a diminished level. When the fetish object is not present, the fetishist often engineers sexual arousal by fantasizing about it. For some fetishists, the fetish object must be used by a partner in a specific way for it to be effective. For example, the genitals must be rubbed by silk, or a partner must wear black garters and high-heeled shoes. In the majority of cases, the person with a fetish poses no danger to others and pursues the use of the fetish object in private, usually through masturbation.

As with many forms of sexual expression, there is a thin line of distinction between fetishism and sexual preferences. At one end is the compulsive, fixated fetishist and at other points along the scale are people who use a sexual aid or are particularly aroused by certain body parts, but do not depend on those things to achieve sexual satisfaction. For example a person is not described as a fetishist if sexual arousal is dependent upon having an attractive partner. Also, a man who is turned on by a woman in black lacy lingerie is not usually labeled as a fetishist as long as this is not the primary focus of his arousal.

The causes of fetishism are not clearly understood. Some learning theorists believe that it develops from early childhood experiences, in which an object was associated with a particularly powerful form of sexual arousal or gratification. Other learning theorists would not focus on early childhood, but on later childhood and adolescence and the conditioning associated with masturbation activity. Psychoanalytical theories of causality focus on concepts of penis worship and castration anxiety. Researchers have shown that in general fetishists have poorly developed social skills, are quite isolated in their lives and have a diminished capacity for establishing intimacy.