Josias Simmler (Josiah Simler; Latin: Iosias Simlerus) (6 November 1530 – 2 July 1576) was a Swiss theologian and classicist, author of the first book relating solely to the Alps.

About 1551 he conceived the idea of making his native land better known by translating into Latin parts of the great Chronik of Johann Stumpf.

With this view he collected materials, and in 1574 published a specimen of his intended work in the shape of a monograph on the Canton of the Valais.

It was re-published by the Elzevirs at Leiden in 1633, and again at Zürich in 1735, while an elaborate annotated edition (prepared by Mr Coolidge), with French translation, notes and appendices, appeared at Grenoble in 1904.

Another fragment of his vast plan was the work entitled De Helvetiorum republica, which appeared at Zürich in 1576, just before his death.