The Bay of Kiel or Kiel Bay (German: Kieler Bucht, ; Danish: Kiel Bugt) is a bay in the southwestern Baltic Sea, off the shores of Schleswig-Holstein in Germany and the islands of Denmark. It is connected with the Bay of Mecklenburg in the east, the Little Belt in the northwest, and the Great Belt in the North.
Maritime traffic entering or leaving the Baltic through the two Belts must enter the bay. Once in, through traffic to the Baltic passes through another strait, the Fehmarn Belt, into the Bay of Mecklenburg, which opens out into the Baltic Sea. In the other direction, traffic can either pass northward through the Great Belt, keeping Langeland on the port side, or enter the Kiel Fjord and traverse the Kiel Canal directly to the mouth of the Elbe River and the North Sea. The Kiel Fjord ends at Kiel, the capital of Schleswig-Holstein.