The toga (/ˈtoʊɡə/, Classical Latin: [ˈt̪ɔ.ɡa]), a distinctive garment of Ancient Rome, was a roughly semicircular cloth, between 12 and 20 feet (3.7 and 6.1 m) in length, draped over the shoulders and around the body. It was usually woven from white wool, and was worn over a tunic. In Roman historical tradition, it is said to have been the favored dress of Romulus, Rome's founder; it was also thought to have originally been worn by both sexes, and by the citizen-military. As Roman women gradually adopted the stola, the toga was recognized as formal wear for male Roman citizens. Women found guilty of adultery and women engaged in prostitution might have provided the main exceptions to this rule.

The type of toga worn reflected a citizen's rank in the civil hierarchy. Various laws and customs restricted its use to citizens, who were required to wear it for public festivals and civic duties.

From its probable beginnings as a simple, practical work-garment, the toga became more voluminous, complex, and costly, increasingly unsuited to anything but formal and ceremonial use. It was and is considered ancient Rome's "national costume"; it had great symbolic value. However, even among Romans, it was hard to put on, uncomfortable and challenging to wear correctly, and never truly popular. When circumstances allowed, those otherwise entitled or obliged to wear it opted for more comfortable, casual garments. It gradually fell out of use, firstly among citizens of the lower class, then those of the middle class. Eventually, it was worn only by the highest classes for ceremonial occasions.

The toga was an approximately semi-circular woollen cloth, usually white, worn draped over the left shoulder and around the body: the word "toga" probably derives from tegere, to cover. It was considered formal wear and was generally reserved for citizens. The Romans considered it unique to themselves, thus their poetic description by Virgil and Martial as the gens togata ('toga-wearing race'). There were many kinds of toga, each reserved by custom to a particular usage or social class.

The toga's most distinguishing feature was its semi-circular shape, which sets it apart from other cloaks of antiquity like the Greek himation or pallium. To Rothe, the rounded form suggests an origin in the very similar, semi-circular Etruscan tebenna. Norma Goldman believes that the earliest forms of all these garments would have been simple, rectangular lengths of cloth that served as both body-wrap and blanket for peasants, shepherds and itinerant herdsmen. Roman historians believed that Rome's legendary founder and first king, the erstwhile shepherd Romulus, had worn a toga as his clothing of choice; the purple-bordered toga praetexta was supposedly used by Etruscan magistrates, and introduced to Rome by her third king, Tullus Hostilius.

In the wider context of classical Greco-Roman fashion, the Greek enkyklon ("circular [garment]") was perhaps similar in shape to the Roman toga, but never acquired the same significance as a distinctive mark of citizenship. The 2nd-century diviner Artemidorus Daldianus in his Oneirocritica derived the toga's form and name from the Greek tebennos, supposedly an Arcadian garment invented by and named after Temenus. Emilio Peruzzi claims that the toga was brought to Italy from Mycenaean Greece, its name based on Mycenaean Greek te-pa, referring to a heavy woollen garment or fabric.

Roman society was strongly hierarchical, stratified and competitive. Landowning aristocrats occupied most seats in the senate and held the most senior magistracies. Magistrates were elected by their peers and "the people"; in Roman constitutional theory, they ruled by consent. In practice, they were a mutually competitive oligarchy, reserving the greatest power, wealth and prestige for their class. The commoners who made up the vast majority of the Roman electorate had limited influence on politics, unless barracking or voting en masse, or through representation by their tribunes. The Equites (sometimes loosely translated as "knights") occupied a broadly mobile, mid-position between the lower senatorial and upper commoner class. Despite often extreme disparities of wealth and rank between the citizen classes, the toga identified them as a singular and exclusive civic body.

Togas were relatively uniform in pattern and style but varied significantly in the quality and quantity of their fabric, and the marks of higher rank or office. The highest-status toga, the solidly purple, gold-embroidered toga picta could be worn only at particular ceremonies by the highest-ranking magistrates. Tyrian purple was supposedly reserved for the toga picta, the border of the toga praetexta, and elements of the priestly dress worn by the inviolate Vestal Virgins. It was colour-fast, extremely expensive and the "most talked-about colour in Greco-Roman antiquity". Romans categorised it as a blood-red hue, which sanctified its wearer. The purple-bordered praetexta worn by freeborn youths acknowledged their vulnerability and sanctity in law. Once a boy came of age (usually at puberty) he adopted the plain white toga virilis; this meant that he was free to set up his own household, marry, and vote. Young girls who wore the praetexta on formal occasions put it aside at menarche or marriage, and adopted the stola. Even the whiteness of the toga virilis was subject to class distinction. Senatorial versions were expensively laundered to an exceptional, snowy white; those of lower ranking citizens were a duller shade, more cheaply laundered.