Johann Ludwig Friedrich Lahrs (11 July 1880 – 13 March 1964) was a German architect and professor.
He worked in Berlin and Charlottenburg until 1908; in 1906 he was awarded the Schinkelpreis in honor of Karl Friedrich Schinkel.
In the same year he designed a regimental memorial at Brandenburg Gate honoring casualties from Königsberg's foot artillery during World War I.
Lahrs remained at the Kunstakademie until 1934, when he retired his professorship after the appointment of Kurt Frick to the academy during Gleichschaltung.
After being expelled from Königsberg in 1945 as a result of World War II, Lahrs settled in Stuttgart.