Joshua Alder (7 April 1792 – 21 January 1867) was a British cheesemonger and amateur zoologist and malacologist. As such, he specialized in the Tunicata, and in gastropods. He was a member of the Natural History Society of Northumberland and Durham, and an early member of the Literary and Philosophical Society of Newcastle upon Tyne, alongside Joseph Swan and Robert Stephenson. He corresponded with Charles Darwin. His drawings are in the collections of the Great North Museum: Hancock and the British Museum.