Köstler, Koestler is a family surname.
Köstler, Koestler:
- Arthur Koestler (1905–1983), a Hungarian political writer
- The Koestler Trust, a charity
- Arthur Koestler, the title of a book by Mark Levene in 1984
- Arthur Koestler/Arrow in the Blue, the title of an autobiography by Arthur Koestler
- Living with Koestler: Mamaine Koestler's Letters 1945-51, a book about Arthur and Mamaine Koestler
- Arthur Koestler: The Story of a Friendship, the title of a book by George Mikes in 1983
- Mamaine Koestler, née Paget (1916–1954), the 2nd wife of Arthur Koestler
- Marie Köstler (1879–1965), Austrian nurse, trade unionist and politician
- Jonathan "John" Koestler, a fictional character in the 2009 film Knowing.