Whales can eat anything from plankton to krill, fish, giant squid or other whales. What a whale eats depends on whether it has teeth or baleen.
Baleen whales have baleen plates that hang from their upper jaws instead of teeth. The whale takes in a huge amount of water, krill or fish, then filters out the food with the baleen. Rorqual whales have grooves or pleats on their throats that expand to hold great volumes of water.
Sperm whales and killer whales have teeth. Sperm whales have been known to dive very deep to catch their prey, the giant squid. The killer whale has a varied diet and eats fish, squids, birds, sea turtles, dolphins and even other whales.