In common law, the doctrine of reception (properly, reception of the common law of England in a colony) refers to the process in which the English law becomes applicable to a British Crown Colony, protectorate, or protected state.
In Commentaries on the Laws of England (Bk I, ch.4, pp 106-108), Sir William Blackstone described the doctrine as follows:
Plantations or colonies, in distant countries, are either such where the lands are claimed by right of occupancy only, by finding them desert and uncultivated, and peopling them from the mother-country; or where, when already cultivated, they have been either gained by conquest, or ceded to us by treaties. And both these rights are founded upon the law of nature, or at least upon that of nations. But there is a difference between these two species of colonies, with respect to the laws by which they are bound. For it hath been held, that if an uninhabited country be discovered and planted by English subjects, all the English laws then in being, which are the birthright of every subject, are immediately there in force... But in conquered or ceded countries, that have already laws of their own, the king may indeed alter and change those laws; but, till he does actually change them, the ancient laws of the country remain, unless such as are against the law of God, as in the case of an infidel country.
(Note: the 'infidel country' reference here was mainly intended to prohibit customs considered barbaric by the British, such as cannibalism, once a territory was colonized, in an age when communications between the British government and her far-flung colonies could take months on end.)
In other words, if an 'uninhabited' territory is colonised by Britain, then the English law automatically applies in this territory from the moment of colonisation; however if the colonised territory has a pre-existing legal system, the native law would apply (effectively a form of indirect rule) until formally superseded by the English law, through Royal Prerogative subjected to the Westminster Parliament.
In practice, it could take years or even decades for the native law in a colony to be gradually superseded by the English law. The legal history of Hong Kong provides an illustration of this point: after the colonization by the British Empire in 1841, the Great Qing Legal Code remained in force for the local Chinese population. Until the end of the 19th Century, Chinese offenders were still executed by decapitation, whereas the British would be put to death by hanging. Even deep into the 20th Century and well after the fall of the Qing dynasty in China, Chinese men in Hong Kong could still practice polygamy by virtue of the Qing Code -- a situation that was ended only with the passing of the Marriage Act of 1971.