Derived from the Italian word graffio (“scratch”), graffiti (“incised inscriptions,” plural but often used as singular) has a long history. For example, markings have been found in ancient Roman ruins, in the remains of the Mayan city of Tikal in Central America, on rocks in Spain dating to the 16th century, and in medieval English churches. During the 20th century, graffiti in the United States and Europe was closely associated with gangs, who used it for a variety of purposes: for identifying or claiming territory, for memorializing dead gang members in an informal “obituary,” for boasting about acts (e.g., crimes) committed by gang members, and for challenging rival gangs as a prelude to violent confrontations. Graffiti was particularly prominent in major urban centres throughout the world, especially in the United States and Europe; common targets were subways, billboards, and walls. In the 1990s there emerged a new form of graffiti, known as “tagging,” which entailed the repeated use of a single symbol or series of symbols to mark territory. In order to attract the most attention possible, this type of graffiti usually appeared in strategically or centrally located neighbourhoods.

To some observers graffiti is a form of public art, continuing the tradition, for example, of the murals (mural) commissioned by the U.S. Works Progress Administration Federal Art Project during the Great Depression and the work of Diego Rivera (Rivera, Diego) in Mexico. Like the murals of these artists, great works of graffiti can beautify a neighbourhood and speak to the interests of a specific community. For example, the graffiti in many Hispanic neighbourhoods in the United States is quite elaborate and is regarded by many as a form of urban art. The question of whether such work is an innovative art form or a public nuisance has aroused much debate.

Graffiti became notoriously prominent in New York City in the late 20th century. Large elaborate multicoloured graffiti created with spray paint on building walls and subway cars came to define the urban landscape. The art world's fascination with artists who functioned outside traditional gallery channels stimulated an interest in this form of self-expression. In the 1980s New York artists such as Keith Haring (Haring, Keith) and Jean-Michel Basquiat (Basquiat, Jean-Michel) gained notoriety for their graffiti and parlayed this recognition into successful careers as painters represented by top galleries.

Most jurisdictions have laws prohibiting graffiti as vandalism, and in some countries punishment is quite severe. For example, in Singapore violators are subject to caning. During the 1980s and '90s many jurisdictions sought ways to eliminate and remove graffiti, fearing that it would otherwise lead to the debasement of the community. Significant resources were allocated for abatement and other clean-up efforts, and some cities even introduced mural programs or “free walls” to provide legal opportunities for urban youths to express their artistic creativity.