Customary law creates universally binding rules. According to the persistent objector doctrine, states have an opportunity to gain an exemption from emerging norms of customary law by opposing an emerging practice before it solidifies into a binding rule of custom. The subsequent objector doctrine instead gives states an opportunity to depart from an already binding custom when other states acquiesce to their departure. This paper examines the effects of the persistent objector and subsequent objector doctrines in the formation and evolution of customary law when heterogeneous states are involved.