The 1978 Calder Cup Playoffs of the American Hockey League began on April 11, 1978. The top three teams from each division qualified for the playoffs. The two division winners earned byes for the Division Semifinals while the other two teams in each division played best-of-5 series. The winners played best-of-7 series with the team that received the first round bye in their division. The winners of each Division Final played a best-of-7 series for the Calder Cup. The Calder Cup Final ended on May 15, 1978 with the Maine Mariners defeating the New Haven Nighthawks four games to one to win the Calder Cup for the second time in team history.
After the 1977–78 AHL regular season, the top three teams from each division qualified for the playoffs. The Maine Mariners finished the regular season with the best overall record. The two division champions earned byes to the Division Finals.
In each round, the team that earned more points during the regular season receives home ice advantage, meaning they receive the "extra" game on home-ice if the series reaches the maximum number of games. There is no set series format due to arena scheduling conflicts and travel considerations.