In law, a duty of care is the legal requirement that a person exercise a reasonable standard of care to prevent injury of others. Privity of contract is not required for a duty of care to exist.
Duty of care may be considered a formalisation of the implicit responsibilities held by an individual towards another individual within society. It is not a requirement that a duty of care be defined by law, but it will often evolve through the jurisprudence of common law.
Individuals who are considered to be professionals within society are often held to a higher standard of care than those who are not. Engineers and doctors will be held to reasonable standards for members of their profession, rather than those of the general public in cases related to their fields.
Breach of duty of care, if resulting in an injury, may subject an individual to liability in tort. Duty of care is an important prerequisite in the tort of negligence, as the duty of care must exist and must have been breached for the tort to occur.
The duty of care between individuals may exist between individuals not related at the current time, but related in some other manner, as defined by common law. For instance, an engineer or construction company involved in erecting a building may be reasonably responsible to tenants inhabiting the building many years in the future. This point is illustrated by the Supreme Court of South Carolina, in its Terlinde v. Neely decision, later cited by the Supreme Court of Canada in Winnipeg Condominium Corporation No. 36 v. Bird Construction Co. :
The plaintiffs, being a member of the class for which the home was constructed, are entitled to a duty of care in construction commensurate with industry standards. In the light of the fact that the home was constructed as speculative, the home builder cannot reasonably argue he envisioned anything but a class of purchasers. By placing this product into the stream of commerce, the builder owes a duty of care to those who will use his product, so as to render him accountable for negligent workmanship.
Duty of care is evident between drivers of automobiles on the road. Each individual driver owes a duty of care to each other to prevent accidents and drive in a reasonable manner. In the case of an automobile accident, drivers not paying attention or driving irresponsibly will have breached that duty of care.
Manufacturers own a duty of care to consumers who ultimately purchase and use the products. In the case of Donoghue v. Stevenson  AC 562 of the House of Lords, Lord Atkin stated:
My Lords, if your Lordships accept the view that this pleading discloses a relevant cause of action you will be affirming the proposition that by Scots and English law alike a manufacturer of products, which he sells in such a form as to show that he intends them to reach the ultimate consumer in the form in which they left him with no reasonable possibility of intermediate examination, and with the knowledge that the absence of reasonable care in the preparation or putting up of the products will result in an injury to the consumer's life or property, owes a duty to the consumer to take that reasonable care.
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