The eight forms of marriage mentioned in the Smritis are paisacha,
  raksasa, gandharva, asura, prajapatya, arsa, daiva, and brahma, listed in an
  ascending order of merit. The sacrament, however, attempts to bless and
  consecrate every possible form of human union. Nuptial ceremonies are
  supposed to impart sanctity to the marital relation.
      First of all, the determination and selection of the couple control and
  shape the institution of sacramental marriage. Normally a person should
  marry in the same varna but outside the same gotra (clan), and pinda
  (consanguinity). Anuloma marriage (in which the wife is of an inferior caste)
  was permitted but not encouraged; pratiloma marriage (in which the husband
  is of an inferior caste), though tolerated early, was later on discouraged and
  banned. Restrictions regarding sagotra and sapinda marriages have been
  invariably observed; their breach is regarded as incest and is legally
  forbidden.
    A marriage sacrament consists of items pertaining to the premarital,
    marital, and postmarital stages. The most important of these are as
    follows:
    Vagdana (betrothal),
    Vara-varana (formal acceptance of the bride–groom),
    Kanya-dana (gift of the bride to the bridegroom by the legitimate
    guardian),
    Vivaha-homa (marriage offerings),
    Panigrahana (clasping the hand),
    Hridaya-sparsa (touching the heart),
    Saptapadi (seven steps symbolic of prosperity and felicity),
    Asmarohana (mounting the stone, symbolic of stability),
    Suryavalokana (looking at the sun, as a witness to the sacrament),
10. Dhruva-darsana (looking at the Pole Star, a symbol of constancy),
11. Triratra-vrata (three nights’ continence),
12. Chaturthi-karma (fourth day ceremony or the formal unification of the
    couple).
      The Hindu marriage which the nuptials symbolise is not a social contract
  in the modern sense of the term,       but a religious institution, a sacrament.