Reservation or affirmative action is a hugely controversial policy in India. While constitutionally mandated and with historians, political scientists and social activists convinced of its need, many resist it and consider it as compromising 'merit' and against the principle of equality of opportunity. How were groups eligible for reservations identified and defined? How were the terms 'depressed classes' and 'backward classes' used in British India and how have they evolved into the constitutional concepts of 'Scheduled Castes', 'Scheduled Tribes', and 'Other Backward Classes' in the present day?