Custom refers to the code of conduct that has the express approval of the community that observes it. In primitive societies, there were no institutions that acted as authority over the people. This led to people organizing themselves to form cohesive groups in order to maintain fairness, equality, and liberty. They started developing rules with coordinated efforts to make decisions. They eventually started recognising the traditions and rituals practiced by the community routinely and formed a systematized form of social regulation. In India, laws relating to marriage and divorce are mostly developed from customs followed by different religious communities. Additionally, several communities belonging to the Scheduled Tribes category have their own customs related to marriage. As a result of that Section 2(2) of the Hindu Marriage Act, 1955 has exempted Scheduled Tribes from the application of this Act. 

Requisites of a valid custom

1. Reasonability: The custom must be reasonable or practical and must conform with the basic morality prevailing in the modern-day society. 
2. Antiquity: It must have been practiced for time immemorial. 
3. Certainty: The custom must be clear and unambiguous on how it should be practiced.  
4. Conformity with statutes: No custom must go against the law of the land. 
5. Continuity in practice: Not only the custom must be practiced for time immemorial, but it should also be practiced without interruption. 
6. Must not be in opposition to public policy: The custom must adhere to the public policy of the state. 
7. Must be general or universal: There must be unanimity in the opinion of the community or place in which it is practiced. Hence, it should be universal or general in its application.