Kästner (transliterated Kaestner) is a German surname. Notable people with the surname include:
Abraham Gotthelf Kästner, (1719-1800), German mathematician
Kästner (crater), a lunar crater
Detlef Kästner (born 1958), German boxer
Erich Kästner (1899–1974), German author
(12318) Kästner asteroid named after Erich Kästner
Erich Kästner (camera designer) (1911–2005), German movie camera designer
Erich Kästner (World War I veteran) (1900–2008), the last known German veteran of the First World War
Peter Kaestner, American ornithologist