Sir Henry Duncan Littlejohn MD LLD FRCSE was a Scottish surgeon, forensic scientist and public health official. He served for 46 years as Edinburgh's first Medical Officer of Health, during which time he brought about significant improvements in the living conditions and the health of the city's inhabitants. He also served as a police surgeon and medical adviser in Scottish criminal cases.

The Ardlamont Murder, which took place in Argyll, Scotland, on 10 August 1893, gave rise to two high-profile court cases: a murder trial in Edinburgh, and a defamation trial in London the following year.