Geoffrey Nielsen Ostergaard (25 July 1926 – 22 March 1990) was a British political scientist best known for his work on the connections between Gandhism and anarchism, on the British cooperative movement, and on syndicalism and workers' control. His books included The Gentle Anarchists: A Study of the Sarvodaya Movement for Non-Violent Revolution in India (1971), coauthored with Melville Currell, and Nonviolent Revolution in India (1985), both dealing with the Sarvodaya movement. He spent the majority of his academic career at the University of Birmingham.

Ostergaard was a lifelong Gandhian. His work on Gandhism sought to reframe the thought of Mohandas Gandhi, Vinoba Bhave and Jayaprakash Narayan in terms of anarchism.

The Gentle Anarchists: A Study of the Sarvodaya Movement for Non-Violent Revolution in India (1971), coauthored with Melville Currell, is a comprehensive study of the Sarvodaya movement. Ostergaard and Currell identify Sarvodaya as an Indian form of anarchism or communitarian socialism and identify points of continuity between Sarvodaya and the anarchist tradition, including rejection of private property and representative government, belief in decentralization and a synthesis of freedom and equality, emphasis on local communities, and support for direct action. The bulk of the book is based on the findings from a survey of the movement's leaders, inquiring into their backgrounds, motivations, political beliefs and attitudes. Reviewing the book in the India Quarterly, Usha Mehta wrote that it evinced "the authors' deep understanding of Indian society and people and of their sympathy for the Sarvodaya movement." In his review for The Journal of Asian Studies, Anthony Parel described The Gentle Anarchists as "a most welcome addition to the literature of modern Indian politics in general and to Gandhian politics in particular". In a review in the Journal of Asian and African Studies, Frank F. Conlon questioned Ostergaard and Currell's methodology but identified the book as "an important first step" that would "reveal much about the condition of sarvodaya in contemporary India and ... stimulate further historical and sociological lines of inquiry." Marvin Dicker, reviewing in Social Forces, similarly questioned Ostergaard and Currell's methodology and noted their sympathy for the movement as a further weakness, but described the book as "a valuable contribution to the literature on social movements."

The Gentle Anarchists was followed by Nonviolent Revolution in India (1985). Ostergaard's account of the Sarvodaya movement here focuses on the period from 1969 to 1977 and on the figures of Bhave and Narayan and their differences, including their respective approaches to the Emergency of 1975–77 and the premiership of Indira Gandhi. Ostergaard argues for the superiority of Narayan's approach over Bhave's, though with significant caveats. Ostergaard also identifies the Sarvodaya movement as the only significant social movement motivated by the belief in nonviolent revolution. Looking to the movement's future, he argues the movement ought to adopt a more overtly anarchistic position including election boycotts and the construction of alternative political institutions from below. Reviewing the book in The Round Table, Antony Copley described the book as "scrupulously fair" and likely to "establish itself as among the most important books to appear on the extraordinary drama of Mrs Gandhi's India." In his review for Our Generation, Robert Graham wrote that "Ostergaard has provided a great service to all those interested in nonviolent social revolution by writing such a thorough and thoughtful analysis", but argued the book fails to provide sufficient background on Indian politics and political groupings.

(Source: Wikipedia.org.)