Johan Theodor Westrin (12 January 1850 – 10 October 1928) was a Swedish archivist and editor of Nordisk familjebok.

After graduating with a PhD degree in 1875, he worked as administrative assistant at the Swedish National Archives, where he in 1897 would be promoted to archivist.

[2] He was co-editor of the first edition of Nordisk familjebok and sole editor of its supplement between 1880–1894 and 1895–1899 respectively.

Since 1906, he was chief editor of the second edition (popularly known as Uggleupplagan, lit.

[2] He was appointed 129th member of the Royal Swedish Academy of Letters on 5 November 1901.