Society for the Diffusion of Useful Knowledge (act. 1826–1846), was founded to bring instruction to a mass readership by Henry Brougham, with a number of his fellow educational reformers. These included James Mill, Zacharay Macaulay, Lord John Russell, and George Birkbeck, founder in December 1823, with Brougham's support, of the London Mechanics' Institute. Many supporters of the new society were also involved in the establishment of the University of London, later called University College, London, of which Brougham and the poet Thomas Campbell (1777–1844) were the originators in 1825. The extension of education to all classes and all ages was the aim of this connected group of reformers, founders also, in the case of Brougham, Birkbeck, and Macaulay, of the Infantile School Society in 1824.

The Society for the Diffusion of Useful Knowledge (SDUK) was proposed at a meeting convened by Brougham in Furnivall's Inn in November 1826. Among the reform-minded lawyers, educators, and politicians present were Thomas Denman, William Tooke, James Loch, and Matthew Davenport Hill, penal reformer (Grobel, 1.17). The aim of the society was to exploit advances in printing and distribution by publishing cheap, informative works to 'supply the appetite which had been created by elementary instruction' (through infants' schools and mechanics' institutes) and 'direct the ability to read to useful ends', as the reforming whig MP Thomas Spring Rice declared at a meeting of the SDUK in May 1828 (The Times, 19 May 1828). It was agreed that the society's publications would avoid party politics and religion, both in order to appeal to the widest audience and to avoid controversy among its members, who, though generally agreeing on questions of political reform, represented a broad spread of religious affiliation, from non-believers to liberal Anglicans and dissenters of various kinds, including the Quaker philanthropist William Allen.

On the whole controversies within the society were avoided. Outside, however, it was perceived as radical and secularist, a close cousin of the new University of London, soon to open in Gower Street to students of all faiths and none who were prevented from graduating at Oxford and Cambridge by their inability to subscribe to the Thirty-Nine Articles of the Church of England. Brougham was the chairman of both the SDUK and the university's first council; Birkbeck, Macaulay, Mill, Russell, Joseph Hume, George Grote, and Isaac Lyon Goldsmid, later first baronet, served on the committees of both institutions. Tories and churchmen seized on the connections, attacking the SDUK, the mechanics' institutes, and the university as a composite entity, calling the university 'the radical infidel college' (W. M. Praed) and 'the Cockney College' (T. E. Hook), and suggesting that together these institutions presented a danger to society by encouraging the masses to aspire above their station. William Thomas Moncrieff's poem 'The March of Intellect, or, Mechanical Academics' is typical; Moncrieff adopts the reformers' rallying cry for his title and pretends to think that workmen will down tools to read improving books, write poetry, and even turn students and professors at the new university:

Oh, Time! how Strange thy changes—Learning's now become mechanical;Scientific men and scholars,Are seized with a sudden panic all.

Moncrieff, Original Collection of Songs

The SDUK, in undertaking the publication of sixpenny treatises in its series the Library of Useful Knowledge from 1827, had 'two main objects in view', namely to 'give the people books which might convey knowledge to uneducated persons, or persons imperfectly educated' and to 'reduce the price of scientific and other useful works to the community generally' (Address to the committee, 1 June 1843). The early treatises, mostly of thirty-two pages, gave up-to-date accounts of various scientific subjects, some written by established experts (David Brewster on optics, for example), but most by rising stars who were taking up the first professorships at the University of London, men like Anthony Todd Thomson, professor of materia medica, the botanist John Lindley, and Augustus De Morgan, the brilliant Cambridge graduate who was appointed to the chair of mathematics at the age of twenty-one and who wrote most of the mathematical articles for the SDUK, which he served as an active committee member until its end in 1846. Among the sixty or so subjects covered by the Library of Useful Knowledge were hydrostatics, hydraulics, pneumatics, geometry, and chemistry. The early treatises sold between 20,000 and 25,000 copies each (Grobel, 2.681–3).

Charles Knight, already interested in producing cheap educational books for a mass market, was engaged as the society's chief publisher, though others were also involved at different times, notably the firm of Baldwin and Cradock, which published the society's maps until it failed in 1837. Chapman and Hall took over the lucrative map publication in 1842, introduced by Charles Dickens, who wrote to Brougham in August 1841 saying his publishers would be glad to fill the vacancy (Letters of Charles Dickens, 2.373). The chief printer was William Clowes, a friend of Knight, who embraced the new technologies and employed the largest number of compositors of any printing firm in the world.

Knight willingly took financial risks on some of the SDUK's loss-making ventures, for example the Penny Cyclopaedia, which he not only published in twenty-nine volumes from 1833 to 1846, but for which he acted as co-editor and author for the early volumes. Knight's contribution to the society was enormous, second only to the astonishing activity on its behalf of Brougham, who combined a number of high-profile careers in the late 1820s and early 1830s—active reforming MP in the debates leading to the passing of the Reform Act in 1832, lord chancellor in Lord Grey's whig administration of 1830–34, principal actor in the affairs of the University of London, eloquent lawyer on the northern circuit, and from 1825 rector of the University of Glasgow. As Walter Bagehot wrote in his survey of Brougham's career in 1857, he could plead a case, drive to the hustings and make speeches, then sit down in his study and pen an article for the Edinburgh Review or an address to his Glasgow students, all in the course of a single day (Bagehot, Biographical Studies, 59–60). Or as Samuel Rogers apparently said when Brougham left a country house party in December 1827, 'This morning Solon, Lycurgis, Demosthenes, Archimedes, Sir Isaac Newton, Lord Chesterfield and a great many more went away in one post chaise' (Diaries of Charles Greville, 21). Brougham was the most famous orator of the day, celebrated for his successful defence of Queen Caroline at her trial in 1820; his influence, not least with the Edinburgh Review, which he had helped to found in 1802, and The Times, whose editor Thomas Barnes was a close friend, ensured that his doings were always in the news. The SDUK, though ridiculed in such ultra-conservative organs as John Bull, was given frequent favourable coverage in The Times.

The society's Library of Useful Knowledge had a flying start with Brougham's introductory treatise, published in 1827 and reaching sales of 42,000 by 1833 (Grobel, 3.681). Entitled A Discourse of the Objects, Advantages, and Pleasures of Science, it offered a clever, breezy survey of the field of science, from mathematics (its usefulness illustrated by the example of a revenue cutter chasing a smuggling ship, the personnel helped by knowing how to calculate when the former will catch the latter by comparing the rate at which each is sailing) to natural philosophy, the solar system, electricity, and—topically—the workings of the steam engine. After a breathtaking run through the whole of science Brougham ends on a Panglossian note, extolling the 'solid benefits' of science in making our everyday lives both 'more agreeable' and morally better.

Encouraged by the success of the early treatises and the financial and moral support of prominent politicians, lawyers, and professors, with a good sprinkling of liberal-minded establishment figures like Edward Maltby, later bishop of Durham, and John Charles Spencer, Viscount Althorp (later third Earl Spencer), the committee rapidly undertook more publishing ventures. The word from supporters around the country in the mechanics' institutes and the SDUK's regional committees was that some of the treatises were too hard for the target audience of ordinary workers to understand (Grobel, 2.387). A Library of Entertaining Knowledge was therefore started in 1828 to complement its Useful counterpart. Its treatises offered instruction on practical subjects in an anecdotal style. Those on insects, birds, and menageries were popular, as was George Lillie Craik's two-volume work of encouragement, The Pursuit of Knowledge under Difficulties (1830–01). Dickens has Sam Weller's father, on seeing his son struggling to compose a valentine, say, 'But wot's that you're a-doin' of? Pursuit of knowledge under difficulties, Sammy?' (Pickwick Papers, chap. 33).

In March 1832 the Penny Magazine was started, a weekly paper of miscellaneous information, remarkable chiefly for its innovative use of woodcut illustrations of high quality for such a cheap publication. The opening article of each number was an account of a historic building—Somerset House, St Paul's Cathedral, the Grande Chartreuse—accompanied by lavish drawings and plans. There were features on animals, on trades and manufacture (sugar, coffee, tea), some short poems, and the occasional review of a recent useful publication. The Penny Magazine sold over 200,000 in its first year, many more than its rival Chambers's Edinburgh Journal, started in the same year (preface to Penny Magazine, vol. 1).

By the mid-1830s the society was in a precarious financial position. The victim of its own success, it had overstretched itself in starting new publications. The Penny Magazine was joined in 1833 by the Penny Cyclopaedia, edited by George Long, first professor of Greek and later of Latin at the University of London. Long also edited the society's Quarterly Journal of Education (1831–5), like the Penny Cyclopaedia a loss-maker. Subscribers were falling off. They had numbered 500 in 1828, but by 1843 were fewer than 40 (Address to the committee, 1 June 1843). The end of the society was hastened by the wildly ambitious plan to publish a universal biographical dictionary. The suggestion was Earl Spencer's; he forced it through in 1841 against much opposition on the committee, many of whose members correctly foresaw that such a huge undertaking would lose money and might never be finished in their lifetime. Amid complaints of delayed payments from hard-pressed contributors, and to the increasing despair of the conscientious editor, Long, seven half-volumes of the Biographical Dictionary struggled into existence between 1842 and 1844, covering between them the letter A.

The Dictionary and the society came to an end with the sudden death of Spencer at the end of 1845. (Long was soliciting entries for the letter B.) The SDUK's affairs were wound up in 1846, twenty years after its energetic start. The best and most important work had been done, as its adherents saw, in its early years, when it had contributed to the larger movements for parliamentary and educational reform. The Steam Intellect Society, as it was nicknamed by Thomas Love Peacock in Crotchet Castle (1831), had associated itself with progress on several fronts, not least with the advent of train travel, and now it had run out of steam. Despite the sneers of those opposed to reform and the susceptibility of the society to parody, however, it played a significant part in nineteenth-century education. Sales figures indicate that its treatises and magazines were widely read. The importance of its publications can be judged by its imitators—no less a publisher than John Murray started his Family Library series in 1829, and Dionysius Lardner, an early contributor to the SDUK, edited the Cabinet Cyclopaedia for Longman from 1830. The society gave work to printers, compositors, and engravers as well as hard-up authors. Most striking of all was the quality of those authors, a dazzling array of intellectual talent collected by Brougham in the early years.