Where they come from
Mindfulness in its modern Western form descends primarily from Theravada Buddhist insight meditation (vipassana), as adapted by Jon Kabat-Zinn in the 1970s for clinical contexts. Tantra descends from a different branch of the Indian contemplative tree — primarily Mahayana Buddhist and Hindu Tantra streams — with a more elaborate ritual and energetic vocabulary, and a more body-engaged orientation.
Where they overlap
Both are contemplative practices. Both center on attention. Both treat the body as a legitimate field of practice. Both work through cumulative daily training rather than peak experiences. Both have substantial empirical research behind their effects on stress, anxiety, and well-being. A mindfulness practitioner can usually recognise what a tantric practitioner is doing, and vice versa.
Where they differ
Mindfulness in its standard clinical form is non-engagement with content — you watch the breath, you watch the body, you do not push or pull anything. Tantra is engagement — you actively work with breath, with energy, sometimes with arousal. Mindfulness is typically seated and silent. Tantra includes sustained breath practices, body-mapping, mantra, sometimes partnered exercises. Mindfulness is content-neutral. Tantra has explicit content (deities, energetic centres, partnered ritual in some lineages).
When to choose mindfulness
When you want something explicitly secular and clinical. When you are starting from zero and want the simplest possible entry point. When you want extensive published research and integration with mainstream healthcare. When you do not want any spiritual or energetic vocabulary at all.
When to choose tantra
When you want a more body-engaged practice. When the issues you are working on are explicitly sexual or relational. When you want a partnered practice, not just solo. When you want a tradition with a longer history and a richer (and stranger) bibliography. When you have done some mindfulness and felt something missing in the body.
Doing both
Many practitioners do both. Daily mindfulness as the foundation, weekly tantric practice as the depth. They reinforce each other rather than conflict. The breath foundation is essentially the same in both traditions; the body-attention is closely related. Adding tantric body-mapping or partnered work to a mindfulness practice does not require abandoning the mindfulness.