Heathenry, also termed Heathenism, contemporary Germanic Paganism, or Germanic Neopaganism, is a modern pagan religion. Scholars of religious studies classify it as a new religious movement. Developed in Europe during the early 20th century, its practitioners model it on the pre-Christian religions adhered to by the Germanic peoples of the Iron Age and Early Middle Ages. In an attempt to reconstruct these past belief systems, Heathenry uses surviving historical, archaeological, and folkloric evidence as a basis, although approaches to this material vary considerably.

Heathenry does not have a unified theology but is typically polytheistic, centering on a pantheon of deities from pre-Christian Germanic Europe. It adopts cosmological views from these past societies, including an animistic view of the cosmos in which the natural world is imbued with spirits. The religion's deities and spirits are honored in sacrificial rites known as blóts in which food and libations are offered to them. These are often accompanied by symbel, the act of ceremonially toasting the gods with an alcoholic beverage. Some adherents also engage in rituals designed to induce an altered state of consciousness and visions, most notably seiðr and galdr, with the intent of gaining wisdom and advice from the deities. Many solitary adherents follow the religion by themselves. Other Heathens assemble in small groups, usually known as kindreds or hearths, to perform their rites outdoors or in specially constructed buildings. Heathen ethical systems emphasize honor, personal integrity, and loyalty, while beliefs about an afterlife vary and are rarely emphasized.

Heathenry's origins lie in the 19th- and early 20th-century Romanticism which glorified the pre-Christian societies of Germanic Europe. Völkisch groups actively venerating the deities of these societies appeared in Germany and Austria during the 1900s and 1910s, although they largely dissolved following Nazi Germany's defeat in World War II. In the 1970s, new Heathen groups established in Europe and North America, developing into formalized organizations. A central division within the Heathen movement emerged surrounding the issue of race. Older groups adopted a racialist attitude—often termed "folkish" within the community—by viewing Heathenry as an ethnic or racial religion with inherent links to a Germanic race. They believe it should be reserved for white people, particularly of northern European descent, and often combine the religion with far right-wing and white supremacist perspectives. A larger proportion of Heathens instead adopt a "universalist" perspective, holding that the religion is open to all, irrespective of ethnic or racial background.

While the term Heathenry is used widely to describe the religion as a whole, many groups prefer different designations, influenced by their regional focus and ideological preferences. Heathens focusing on Scandinavian sources sometimes use Ásatrú, Vanatrú, or Forn Sed; practitioners focusing on Anglo-Saxon traditions use Fyrnsidu or Theodism; those emphasising German traditions use Irminism; and those Heathens who espouse folkish and far-right perspectives tend to favor the terms Odinism, Wotanism, Wodenism, or Odalism. Scholarly estimates put the number of Heathens at no more than 20,000 worldwide, with communities of practitioners active in Europe, the Americas, and Australasia.

Scholars of religious studies classify Heathenry as a new religious movement, and more specifically as a reconstructionist form of modern Paganism. Heathenry has been defined as "a broad contemporary Pagan new religious movement (NRM) that is consciously inspired by the linguistically, culturally, and (in some definitions) ethnically 'Germanic' societies of Iron Age and early medieval Europe as they existed prior to Christianization", and as a "movement to revive and/or reinterpret for the present day the practices and worldviews of the pre-Christian cultures of northern Europe (or, more particularly, the Germanic speaking cultures)".

Practitioners seek to revive these past belief systems by using surviving historical source materials. Among the historical sources used are Old Norse texts associated with Iceland such as the Prose Edda and Poetic Edda, Old English texts such as Beowulf, and Middle High German texts such as the Nibelungenlied. Some Heathens also adopt ideas from the archaeological evidence of pre-Christian northern Europe and folklore from later periods in European history. Among many Heathens, this material is referred to as the "Lore" and studying it is an important part of their religion. Some textual sources nevertheless remain disputed as a means of "reconstructing" pre-Christian belief systems, because they were written by Christians and only discuss pre-Christian religion in a fragmentary and biased manner. The anthropologist Jenny Blain characterises Heathenry as "a religion constructed from partial material", while the religious studies scholar Michael Strmiska describes its beliefs as being "riddled with uncertainty and historical confusion", thereby characterising it as a postmodern movement.

The ways in which Heathens use this historical and archaeological material differ; some seek to reconstruct past beliefs and practices as accurately as possible, while others openly experiment with this material and embrace new innovations. Some, for instance, adapt their practices according to unverified personal gnosis (UPG) that they have gained through spiritual experiences. Others adopt concepts from the world's surviving ethnic religions as well as modern polytheistic traditions such as Hinduism and Afro-American religions, believing that doing so helps to construct spiritual world-views akin to those that existed in Europe prior to Christianization. Some practitioners who emphasize an approach that relies exclusively on historical and archaeological sources criticize such attitudes, denigrating those who practice them using the pejorative term "Neo-Heathen".

Some Heathens seek out common elements found throughout Germanic Europe during the Iron Age and Early Middle Ages, using those as the basis for their contemporary beliefs and practices. Conversely, others draw inspiration from the beliefs and practices of a specific geographical area and chronological period within Germanic Europe, such as Anglo-Saxon England or Viking Age Iceland. Some adherents are deeply knowledgeable as to the specifics of northern European society in the Iron Age and early medieval periods; however for most practitioners their main source of information about the pre-Christian past is fictional literature and popular accounts of Norse mythology. Many express a romanticized view of this past, sometimes perpetuating misconceptions about it; the sociologist of religion Jennifer Snook noted that many practitioners "hearken back to a more epic, anachronistic, and pure age of ancestors and heroes".