New Age is a range of spiritual or religious practices and beliefs that rapidly grew in Western society during the early 1970s. Its highly eclectic and unsystematic structure makes a precise definition difficult. Although many scholars consider it a religious movement, its adherents typically see it as spiritual or as a unification of mind, body, and spirit, and rarely use the term New Age themselves. Scholars often call it the New Age movement, although others contest this term and suggest it is better seen as a milieu or zeitgeist.

As a form of Western esotericism, the New Age drew heavily upon esoteric traditions such as the occultism of the eighteenth and nineteenth centuries, including the work of Emanuel Swedenborg and Franz Mesmer, as well as Spiritualism, New Thought, and Theosophy. More immediately, it arose from mid-20th-century influences such as the UFO religions of the 1950s, the counterculture of the 1960s, and the Human Potential Movement. Its exact origins remain contested, but it became a major movement in the 1970s, at which time it was centered largely in the United Kingdom. It expanded widely in the 1980s and 1990s, in particular in the United States. By the start of the 21st century, the term New Age was increasingly rejected within this milieu, with some scholars arguing that the New Age phenomenon had ended.

Despite its eclectic nature, the New Age has several main currents. Theologically, the New Age typically accepts a holistic form of divinity that pervades the universe, including human beings themselves, leading to a strong emphasis on the spiritual authority of the self. This is accompanied by a common belief in a variety of semi-divine non-human entities such as angels, with whom humans can communicate, particularly by channeling through a human intermediary. Typically viewing history as divided into spiritual ages, a common New Age belief posits a forgotten age of great technological advancement and spiritual wisdom that declined into periods of increasing violence and spiritual degeneracy, which will now be remedied by the emergence of an Age of Aquarius, from which the milieu gets its name. There is also a strong focus on healing, particularly using forms of alternative medicine, and an emphasis on unifying science with spirituality.

The dedication of New Agers varied considerably, from those who adopted a number of New Age ideas and practices to those who fully embraced and dedicated their lives to it. The New Age has generated criticism from Christians as well as modern Pagan and Indigenous communities. From the 1990s onward, the New Age became the subject of research by academic scholars of religious studies.

One of the few things on which all scholars agree concerning New Age is that it is difficult to define. Often, the definition given actually reflects the background of the scholar giving the definition. Thus, the New Ager views New Age as a revolutionary period of history dictated by the stars; the Christian apologist has often defined new age as a cult; the historian of ideas understands it as a manifestation of the perennial tradition; the philosopher sees New Age as a monistic or holistic worldview; the sociologist describes New Age as a new religious movement (NRM); while the psychologist describes it as a form of narcissism.

The New Age phenomenon has proved difficult to define, with much scholarly disagreement as to its scope. The scholars Steven J. Sutcliffe and Ingvild Sælid Gilhus have even suggested that it remains "among the most disputed of categories in the study of religion".

The scholar of religion Paul Heelas characterised the New Age as "an eclectic hotch-potch of beliefs, practices, and ways of life" that can be identified as a singular phenomenon through their use of "the same (or very similar) lingua franca to do with the human (and planetary) condition and how it can be transformed." Similarly, the historian of religion Olav Hammer termed it "a common denominator for a variety of quite divergent contemporary popular practices and beliefs" that have emerged since the late 1970s and are "largely united by historical links, a shared discourse and an air de famille". According to Hammer, this New Age was a "fluid and fuzzy cultic milieu". The sociologist of religion Michael York described the New Age as "an umbrella term that includes a great variety of groups and identities" that are united by their "expectation of a major and universal change being primarily founded on the individual and collective development of human potential."

The scholar of religion Wouter Hanegraaff adopted a different approach by asserting that "New Age" was "a label attached indiscriminately to whatever seems to fit it" and that as a result it "means very different things to different people". He thus argued against the idea that the New Age could be considered "a unified ideology or Weltanschauung", although he believed that it could be considered a "more or less unified 'movement'." Other scholars have suggested that the New Age is too diverse to be a singular movement. The scholar of religion George D. Chryssides called it "a counter-cultural Zeitgeist", while the sociologist of religion Steven Bruce suggested that New Age was a milieu; Heelas and scholar of religion Linda Woodhead called it the "holistic milieu".