Ctesibius or Ktesibios or Tesibius (working 285–222 BC) of Alexandria (Greek Κτησίβιος) was an inventor and mathematician in ancient Greece. His contributions to mathematics and science are second only to Archimedes. He wrote the first treatises on the science of compressed air and its uses in pumps (and even a cannon).

Ctesibius is a small lunar impact crater that is located near the equator, on the far side of the Moon. It lies between the larger Abul Wáfa crater to the west and the slightly smaller Heron crater to the east.