Frederick Soddy (2 September 1877–22 September 1956) was an English radiochemist who explained, with Ernest Rutherford, that radioactivity is due to the transmutation of elements, now known to involve nuclear reactions. He received the Nobel Prize for Chemistry in 1921.

In 1900 he became a demonstrator in chemistry at McGill University in Montreal, Quebec, Canada, where he worked with Ernest Rutherford on radioactivity.
In 1903, with Sir William Ramsay at University College London, Soddy verified that the decay of radium produced alpha particles composed of positively charged nuclei of helium.
From 1904 to 1914, Soddy was a lecturer at the University of Glasgow and while there he showed that uranium decays to radium.
In 1914 he was appointed to a chair at the University of Aberdeen, where he worked on research related to World War I.
In 1919 he moved to Oxford University as Dr Lee's Professor of Chemistry, where, in the period up till 1936, he reorganized the laboratories and the syllabus in chemistry.
He received the 1921 Nobel Prize in chemistry for his research in radioactive decay and particularly for his formulation of the theory of isotopes.
Soddy published The Interpretation of Radium (1909) and Atomic Transmutation (1953).
He died in Brighton, England.