The short answer
Tantra emerged from inside Hindu and Buddhist religious frameworks, and many lineages remain explicitly religious to this day. But the underlying practices — breath, attention, body-mapping, mantra, partnered intimacy as contemplation — can be done in a fully secular context, and increasingly are. Whether your practice is religious is a choice you make, not a property of the tradition itself.
Where the religious roots actually are
Classical Tantra developed within Hindu and Buddhist religious cosmology in India between the 5th and 12th centuries CE. The foundational texts assume a religious worldview — devotion to particular deities, transmission from a guru, ritual offerings, belief in subtle-body energetics. If you read a 9th-century Kashmiri Shaiva text, you cannot extract the practice from the religion without losing some of the meaning. The religion is the architecture inside which the practice was originally lived.
How modern teachers handle this
Different teachers solve this differently. Some retain the full classical religious framework — initiation, deity practice, mantra — and teach it that way. Some have removed the religious framework entirely and teach the practices in secular clinical or somatic language. Some hold both at once, offering the religious framing as optional context rather than requirement. None of these approaches is wrong. They serve different students.
For people leaving high-control religion
Many people who leave evangelical Christianity, Mormonism, Orthodox Jewish communities, or other high-control religious traditions arrive at tantra wary of anything that looks like religion. For these people we strongly recommend the secular contemporary versions. The goal is not to replace your inherited dogma with someone else's. The goal is to recover the body-based intelligence your inherited dogma made you mistrust.
For people drawn to the religious dimension
For people who feel the pull toward devotion, ritual, mantra — the classical traditions are intact and accessible. Find a teacher in a recognised lineage. Be patient with the language. Most religious-tantric traditions have a long apprenticeship before the more advanced practices are even named. That is a feature, not a bug.