Under the Indian Contract Act, 1872, the consideration or object of an agreement is unlawful when it is 'forbidden by law'. This rule appears in:

Section 23 of the Indian Contract Act enumerates the conditions under which the consideration or object of an agreement is unlawful. It lists 'forbidden by law', 'defeats the provisions of any law', 'fraudulent', 'injury to person or property', 'immoral' and 'opposed to public policy' as grounds that make consideration or object unlawful. Section 24 deals with part-illegality and Section 25 with void agreements without consideration. Section 26 voids agreements in restraint of marriage. The provision is foundational because any agreement founded on unlawful consideration is void ab initio.