Theoctistus or Theoktistos (Greek: Θεόκτιστος) can refer to:
- Monk Theoktistos (died 800), the hegumen of Sicilian Kucuma, commemorated as an Eastern Orthodox saint.
- Theoctistus of Alexandria, a sea captain, martyr, saint, and companion of Faustus, Abibus and Dionysius of Alexandria
- Theoctistus of Palestine (died 451 or 467), aka Venerable Theoctistus (Theoktistos) of Palestine, Byzantine monk, hermit and Orthodox saint, active in Palestine, companion of Saint Euthymius the Great with whom he established a monastery, commemorated on September 3
- Theoktistos (magistros) (fl. 802–821), senior Byzantine official
- Theoktistos Bryennios (ca. 842), Byzantine general
- Theoktistos, chief minister and regent of the Byzantine Empire from 842 to 855
- Theoktistos the Stoudite, 14th-century Byzantine ecclesiastical writer
- Theoctistus of Caesarea, bishop; see Origen
- Theoctistus of Naples, Duke of Naples in 818-821
- Teoctist Arăpaşu (born Toader Arăpaşu, 1915-2007), Patriarch of the Romanian Orthodox Church from 1986 to 2007
- Teoctist I of Moldavia (ca. 1410-1477), Metropolitan of Moldavia from 1453 to 1477