Martijn Theodoor Houtsma (15 January 1851, in Irnsum, Friesland – 9 February 1943, in Utrecht), often referred to as M. Th. Houtsma, was a Dutch orientalist and professor at the University of Utrecht. He was a fellow of the Royal Netherlands Academy of Arts and Sciences, and a leading expert on the history of the Seljuks. He remains best known for his work as editor of the first edition (1913–38) of the standard encyclopedic reference work on Islam, the Encyclopaedia of Islam. Life and works Houtsma was the son of Otto Evertz Houtsma, a wood miller and later the Mayor of Rauwerderhem in Irnsum, and Feikje Maria Petronella Horreüs Laurman. He attended the Latin school at Dokkum before enrolling at the University of Leiden for a degree in theology in 1868 which he soon combined with the study of Eastern languages. Among his tutors at Leiden were Antonie Rutgers, Reinhart Dozy, Michael Jan de Goeje and Abraham Kuenen. He graduated in 1875 as a Doctor of Theology from Leiden where he wrote his dissertation entitled De strijd over het dogma in den Islam tot op el-Ash'ari (The Struggle Over Dogma in Islam Up to Al-Ashari), a work offering a systematic study of dogmatic developments in Islam from the time of Muhammad up to c.950. In 1874 Houtsma became a lecturer in Hebrew at Leiden and between 1874 and 1890 worked as the Assistant Keeper of the Oriental Manuscripts at the University Library. During this time he focused on the study of Persian and Turkish, and on the history of the Seljuks in particular. For a period of time he was also a lecturer in Persian and Turkish. In 1890, he was appointed the professor of Hebrew and Israelite antiquities at the University of Utrecht and elected as a member of the Royal Academy of Sciences. At Utrecht, Houtsma used his position mainly for the organisation of Islamic research, though his abiding interest with the study of the Old Testament continued. In 1898, he was appointed Chief Editor of the project initiated by the International Orientalist Congress to produce an encyclopaedia of Islam. This resulted in the publication of the first edition of the Encyclopaedia of Islam whose first volume appeared in 1913 in parallel English, German, and French editions. He retired from professorship in 1917 but stayed on at Utrecht. Houtsma published the index volume to the Oriental Catalogue of