Sir Christopher Kelk Ingold BEM FRS[1] (28 October 1893 – 8 December 1970) was a British chemist based in Leeds and London.

His groundbreaking work in the 1920s and 1930s on reaction mechanisms and the electronic structure of organic compounds was responsible for the introduction into mainstream chemistry of concepts such as nucleophile, electrophile, inductive and resonance effects, and such descriptors as SN1, SN2, E1, and E2.

Starting around 1926, Ingold and Robert Robinson carried out a heated debate on the electronic theoretical approaches to organic reaction mechanisms.

[11] In 1920, Ingold was awarded the British Empire Medal (BEM) for his wartime research involving "great courage in carrying out work in a poisonous atmosphere, and risking his life on several occasions in preventing serious accidents,"[12] though he subsequently never discussed the award or this period in his life.

The chemistry department of University College London is now housed in the Sir Christopher Ingold building, opened in 1969.