Westernization or Westernisation (see spelling differences), also occidentalization or occidentalisation (from the Occident, meaning the Western World; see "occident" in the dictionary), is a process whereby societies come under or adopt Western culture in such matters as industry, technology, law, politics, economics, lifestyle, diet, language, alphabet, religion, philosophy, and/or values. Westernization has been a pervasive and accelerating influence across the world in the last few centuries. It is usually a two-sided process, in which Western influences and interests themselves are joined by a wish of at least parts of the affected society to change towards a more Westernised society, in the hope of attaining Western life or some aspects of it.

Westernization can also be related to the process of acculturation and/or enculturation. Acculturation refers to the changes that occur within a society or culture when two different groups come into direct continuous contact. After the contact, changes in cultural patterns within either or both cultures are evident. In popular speech, Westernization can also refer to the effects of Western expansion and colonialism on native societies.