Leonard Trelawny Hobhouse, FBA (8 September 1864 – 21 June 1929) was a British liberal political theorist and sociologist, who has been considered one of the leading and earliest proponents of social liberalism. His works, culminating in his famous book Liberalism (1911), occupy a seminal position within the canon of New Liberalism.

He worked both as an academic and a journalist, and played a key role in the establishment of sociology as an academic discipline; in 1907 he shared, with Edward Westermarck, the distinction of being the first professor of sociology to be appointed in the United Kingdom, at the University of London. He was also the founder and first editor of The Sociological Review. His sister was Emily Hobhouse, a British welfare activist.

Hobhouse was born in St Ive, near Liskeard in Cornwall, the son of Reginald Hobhouse, an Anglican clergyman, and Caroline Trelawny. He attended Marlborough College before reading Greats at Corpus Christi College, Oxford, where he graduated with a first-class degree in 1887. Upon his graduation, Hobhouse remained at Oxford as a prize fellow at Merton College before becoming a full fellow at Corpus Christi. Taking a break from academia between 1897 and 1907, Hobhouse worked as a journalist (including a stint with the Manchester Guardian) and as the secretary of a trade union. In 1907, Hobhouse returned to academia, accepting the newly created chair of sociology at the University of London, titled the Martin White Professor of Sociology, where he remained until his death in 1929.

Hobhouse was also an atheist from an early age, despite his father being an archdeacon. He believed that rational tests could be applied to values and that they could be self-consistent and objective.

Hobhouse was never religious. He wrote in 1883 that he was "in politics... a firm radical. In religion... an (if possible yet firmer) agnostic". In terms of his political and philosophical views, Hobhouse was Gladstonian; a devoted follower of the philosopher John Stuart Mill; and an admirer of John Morley, Bradlaugh; and Sir Charles Dilke, 2nd Baronet. These influences led him to various feminist, democratic and secularist political stances. He often proposed republican and democratic motions at debating societies while he was at school.

Hobhouse was important in underpinning the turn-of-the-century 'New Liberal' movement of the Liberal Party under leaders like H. H. Asquith and David Lloyd George. He distinguished between property held 'for use' and property held 'for power'. Governmental co-operation with trade unions could therefore be justified as helping to counter the structural disadvantage of employees in terms of power. He also theorised that property was acquired not only by individual effort but by societal organisation. Essentially, wealth had a social dimension and was a collective product. That means that those who had property owed some of their success to society and thus had some obligation to others. He believed that to provide theoretical justification for a level of redistribution provided by the new state pensions.

Hobhouse disliked Marxist socialism and described his own position as liberal socialism and later as social liberalism. Hobhouse thus occupied a particularly-important place in the intellectual history of the Liberal Democrats.

His work also presents a positive vision of liberalism in which the purpose of liberty is to enable individuals to develop, not solely that freedom is good in itself. Hobhouse said that coercion should be avoided not for lack of regard for other people's well-being but because coercion is ineffective at improving their lot.