Sierk Coolsma (Dutch pronunciation: [sir(ə)ˈkoːlsmaː]; 26 January 1840 – 20 March 1926) was a Dutch Protestant missionary who wrote extensively on the Sundanese language. Born in the Netherlands, he became a missionary in his early twenties and arrived in the Dutch East Indies in 1865. First tasked to Cianjur, he studied Sundanese in more detail than his contemporaries, gaining an appreciation for the language. Further missionary activities in Bogor, begun in 1869, were a failure, and in 1873 he was tasked with translating the New Testament into Sundanese. Although the Sundanese people highly valued poetry, he did the translation in prose hoping that it would help readers entertain new ideas.