In tort law, a duty of care is a legal obligation imposed on an individual requiring that they adhere to a reasonable standard of care while performing any acts that could foreseeably harm others. In order to proceed with an action in negligence, the plaintiff must be able to articulate a duty of care imposed by law which the defendant has breached. In turn, breaching a duty may subject an individual to liability in tort.
Duty of care may be considered a formalization 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, though it will often develop through the jurisprudence of common law. For example, 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.
The duty of care may exist between individuals with no current direct relationship (familial or contractual or otherwise), but eventually become related in some 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 275 S.C. 395, 271 S.E.2d 768 (1980) decision, later cited by the Supreme Court of Canada in Winnipeg Condominium Corporation No. 36 v. Bird Construction Co.  1 S.C.R. 85:
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.
At common law, in the case of landowners, the extent of their duty of care to those who came on their premises varied depending on whether a person was classified as a trespasser, licensee, or invitee. This rule was eventually abolished in some common law jurisdictions. For example, England enacted the Occupiers Liability Act 1957. Similarly, in the 1968 landmark case of Rowland v. Christian, the Supreme Court of California replaced the old classifications with a general duty of care to all persons on one's land, regardless of their status.
Duty of care is evident between drivers of automobiles on the road. Each individual driver owes a duty of care to each of the other surrounding people - motorists, cyclists and pedestrians - 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.
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.