The Kama Sutra in one paragraph
The Kama Sutra is a Sanskrit treatise written by Vatsyayana in the 2nd-3rd century CE. Its name means roughly "treatise on desire/pleasure." It is one of three classical Sanskrit "purusartha" texts — Dharma Sutra (duty), Artha Sutra (wealth and statecraft), Kama Sutra (pleasure). It is best understood as a manual of civilised pleasure for educated urban householders, including chapters on courtship, marriage, household management, and yes, sexual technique.
Tantra in one paragraph
Tantric texts are a body of literature written between roughly the 5th and 12th centuries CE, in both Hindu and Buddhist traditions, concerned with practices for spiritual awakening that use the body and the senses as the field of practice. The tantric canon is large, varied, and includes texts on mantra, ritual, visualisation, subtle-body energetics, and (in some lineages) partnered sexual practice as a contemplative discipline.
Where they actually differ
Intent: Kama Sutra is about pleasure as a legitimate human good in itself. Tantra is about awakening, with pleasure (in some lineages) as one tool among many. Era: Kama Sutra is older by 200-300 years. Audience: Kama Sutra was written for the worldly householder; classical tantra for spiritual aspirants under teacher guidance. Sexual content: The Kama Sutra has explicit technical sex content (positions, types of kissing, etc.); most classical tantric texts do not — the sexual practices that exist are framed as sacred ritual under specific conditions.
Where they overlap
Both treat the body as a legitimate field of attention. Both come from the same broad Indian intellectual milieu. Both acknowledge sexuality as a serious subject worthy of study. Both have been heavily caricatured in Western popular culture. Most modern Western "tantric sex" programs blend both traditions without distinguishing them — which is fine for practical purposes but inaccurate as scholarship.