Cephissus (Greek Κήφισσος: Kifissós, Kephissós, or Kêphissos) or Cephisus (Greek Κήφισος: Kêphisos) the name of several rivers in Greece:

• Cephissus (Boeotia), a river arising in Phocis and flowing through northern Boeotia into Lake Copais.
• Cephissus (Athenian plain), a river in Attica flowing through the Athenian plain.
• Cephissus (Eleusinian plain), a river of Attica flowing through the Eleusinian plain. Pausanias (1.38.4) claims it flows more violently than the other Cephissus of the Athenian plain.
• Cephissus (Argolis), a river of Argolis, tributary of the Inachus. According to Pausanias (2.15.5) the rivers Inachus, Cephissus, and Asterion judged between Poseidon and Hera as to who should own Argos. They judged for Hera, whereupon Poseidon dried up the land so that the rivers that flow there provide little water, except after rain, and dry up in the summer.
• Cephissus (Salamis), a river in Salamis.
• Cephissus (Corinth), a former river which Pausanias (2.20.6) says was destroyed by Poseidon but which can still be heard flowing under the earth at a sanctuary to Cephissus in Corinth.

Cephissus was also a man changed into a sea monster by Apollo.