Furtum was a delict of Roman law comparable to the modern offence of theft (as it is usually translated) despite being a civil and not criminal wrong. In the classical law and later, it denoted the contrectatio ("handling") of most types of property with a particular sort of intention – fraud and in the later law, a view to gain. It is unclear whether a view to gain was always required or added later, and, if the latter, when. This meant that the owner did not consent, although Justinian broadened this in at least one case. The law of furtum protected a variety of property interests, but not land, things without an owner, or types of state or religious things. An owner could commit theft by taking his things back in certain circumstances, as could a borrower or similar user through misuse.

The Romans distinguished between "manifest" and "non-manifest" theft based on how close to the scene of the crime the thief was caught, although exactly where the line was, was debated by jurists. Under the Twelve Tables, death or flogging could be expected for a manifest thief, later changed to damages of four times the thing. The penalty for non-manifest theft was two times. There were complementary actions against the occupier of the property where the stolen goods were found, if the defendant did not bring the thing to court or refused a search. Vindicatio or condictio could also be undertaken by the owner of the thing, in addition to an action under furtum.

Contrectatio meant "handling" and was established as the prohibited action associated with furtum before the end of the Roman Republic. Furtum had in the early and mid-Republic required the carrying away of a thing. This was widened and there are several examples from the classical Rome and later where it is even hard to find physical contact in any sense. Contrectatio extended to dealing with the thing as if the owner, and "physical interference" can be considered a more accurate term than just touching. The idea of furtum, and conrectatio in particular, broadened during the republic to complement the narrowly defined Lex Aquilia. This did, for example, include using a borrowed thing in a way which went beyond that agreed with the lender (furtum usus), such as borrowing a horse and riding it for longer than agreed. During the Republic, no distinction was made in language between furtum usus and furtum in general. Contrectio included what might be thought of as fraud: knowingly accepting a wrongful payment, or embezzlement, for example. The case of wrongful payment is problematic, because a mistaken payment still transferred ownership; it seems contradictory that the receiver was granted ownership and still liable for theft. To accept a thing as a pledge knowing that it did not belong to the pledgor was also furtum – not merely acting as an accomplice. Plautus, a playwright, suggests that failing to report a theft after the fact was furtum, but this should not be assumed. The development of contrectio as the preferred prohibited act accompanied that of the criminal law, the actio doli (for fraud) and the Aquilian actions.

An accomplice could be sued if he had provided help ope consilio – a physical act relating to the method of execution, rather than mere encouragement. It appears that Labeo was the first to require help or advice, and earlier sources suggest that both help and advice was required. Labeo's version was certainly entrenched by the early second century AD. An accomplice was treated as if he himself had committed the crime. Only one person needed to have handled the thing for all wrongdoers to be liable. Republican jurists were harder on accomplices than later jurists under the Roman Empire. Indeed, Ulpian considers the unwitting accomplice, who accidentally knocks out of the victim's hand some coins which are then stolen, an accomplice to the theft. Some commentators have gone as far to say that the veteres ("ancients") may not have even required a third party to remove the coins, as long as they were otherwise lost to the owner.

The requisite intention (sometimes described as "animus furandi") was a fraud (fraudulosa). The act had to be against the will of the owner. The prospective thief also had to believe that he did not have the owner's consent. This is confirmed in Gaius in the case of the slave who alerts his master to the fact that he has been bribed by another to steal from his master. The owner now consents to the thief's appropriation so he can be caught in the act, and therefore prevents the crime actually occurring. Justinian, however, reverses this distinction for public policy reasons, and thus creates rather an anomaly. The acts had to be done deliberately, not merely negligently.

Intention to make a gain was probably necessary in Justinian's time. It is thought that this was the case during classical Rome, as well: an example of Gaius is quoted in the Digest, and implies so; Sabinus is quoted by Gellius as including such a condition. It is not entirely clear, however. This rule complements the existence of damnum iniuria datum. In a notable example, a man, acting dishonestly, calls a mule-driver to court frivolously, which caused the mules to be lost. Although this was classed as theft, there is no obvious intention to make a gain. This may have been because if the mules were lost, they had necessarily been stolen by someone. That being the case, the perpetrator could be held as an accomplice. Damnum iniuria datum focussed on wrongful damage to property. It is then, in form, more appropriate an action than furtum in cases where a loss has been caused, although the penalty nature of furtum did mean it could result in a higher payment.

Infantes (young children) and furiosi ("lunatics") were considered incapable of formulating the necessary intention and could therefore not commit furtum.

The thing must be movable, if it is to be stolen. Whilst an immovable thing cannot be carried away, the pre-classical extension to other types of interference with property means that immovable were not by their nature excluded. Gaius indicates that certain veteres ("ancients") believed that land could be stolen. This was also the view of Sabinus, but it was rejected by other classical jurists. A thing separated from the land could be stolen, however. Usucapio was particularly important with regard to land, and therefore the exclusion may have been retained to help the good faith possessor of land to usucapt. Res sanctae and religiosia were covered by separate delicts; and one could not steal a res nullius. One can commit furtum of one's own property, for example by taking back a thing pledged to a creditor, or by secretly reclaiming one's own thing from a good faith possessor. Free persons could also be stolen, for example, children; a wife in manu; indicati and auctorati. This was probably a hang-over from a time when dominium (ownership), manus and potestas were indistinct and not formally separate. Res hereditariae could not be stolen, perhaps for want of a suitable plaintiff with a sufficient interest.