The impetus for this thesis was based on a premise that the Provincial Governors of British India have been given too little credit by history for their involvement in the development, in particular, of all-India governmental policy and for the consequential effects. In order to explore this view and to determine the nature and impact of the Governors' contribution it was necessary to select major, discrete policy areas for examination. Lord Irwin's era was chosen because of its importance in the evolution of India's constitutional development, and thus that it permitted an analysis of the Governors' attitude towards and influence on Indian nationalism. The policy areas selected, under the heading of Government and Administration, for this examination and analysis were the Montford Reforms and dyarchy, the Simon Commission, Irwin's Dominion Status Declaration and the first Round Table Conference. Under the heading of Nationalism and Emergency the Governors' contributions to British policy responses towards communal tensions, the detenu issue, Communism, terrorism, Bardoli, Gandhi, civil disobedience and insurgency were identified. This work is introduced by an exposition of the Governors' constitutional, legal and personal standing in India. The research and analysis has confirmed the critical and extensive nature of the Governors' contribution to all-India policy, and hence to the decisions and actions decided upon at the Viceregal and metropolitan levels. The degree of influence over Lord Irwin exercised by the Indian Civil Service Provincial Governors in contrast to the Presidential Governors was noted. Some Governors exercised more influence than others. The importance of the ICS Governors to Irwin stemmed to a significant degree from their expertise developed through long Indian experience. It was identified that following the liberal Montford Reforms there was a power shift towards the Provinces, that the Governors were established as key interlocutors with Indian nationalism and formed a vital link between it and the Government of India. Some Governors in their interaction with nationalism reflected a progressive attitude consistent with the intent of the Montford Reforms. This thesis establishes that Irwin alone did not rule British India, which in many respects can safely be described as a Governors' Raj.