Sir Denys Lasdun (8 September 1914–11 January 2001) was an eminent English architect of the 20th century, particularly associated with the Modernist design of the Royal National Theatre on London's South Bank of the River Thames.

Like other Modernist architects, including Sir Basil Spence and Peter and Alison Smithson, Lasdun was much influenced by Le Corbusier and Ludwig Mies van der Rohe, but there was a gentler, more classical influence, too, from the likes of Nicholas Hawksmoor. Before and after Second World War service in the army, he worked for a while with Berthold Lubetkin 's Tecton practice, after which he set up his own London-based practice.

While he is esteemed by many of those who like Modernist architecture, some of his work is controversial, and even intensely disliked by those who do not.

Lasdun’s projects included:

• Fitzwilliam College, Cambridge (1959-60)
• Royal College of Physicians, London (1960-64)
• student housing at the University of East Anglia, Norwich (1962-68)
• Keeling House (a Grade II* listed building) and Bradley House , Bethnal Green, east London
• Institute of Education, and the library of the School of Oriental and African Studies, Bloomsbury, London
• Royal National Theatre, London (1967-76)
• first phase of the European Investment Bank, Luxembourg (1974-80)