Defence (defense in the United States) in ice hockey is a player position whose primary responsibility is to prevent the opposing team from scoring. They are often referred to as defencemen, defensemen, D, D-men or "blueliners" (the latter a reference to the blue line in ice hockey which represents the boundary of the offensive zone; defencemen generally position themselves along the line to keep the puck in the zone). They were once called cover-point.

In regular play, two defencemen complement three forwards and a goaltender on the ice. Exceptions include overtime during the regular season and when a team is shorthanded (i.e. has been assessed a penalty), in which two defencemen are typically joined by only two forwards and a goaltender.

Each year the NHL, the premier ice hockey league in the world, presents the James Norris Memorial Trophy to the best defenceman in the league. Bobby Orr of the Boston Bruins – an eight-time Norris Trophy recipient – is often considered to be the greatest defenceman in NHL and ice hockey history. In addition to his Norris Trophy honours, he is the only defenceman in NHL history to capture the Art Ross Trophy as the league's leading scorer. In 1998, Orr was selected as the best defenceman of all-time (second overall player behind Wayne Gretzky) in The Hockey News' Top 100 NHL Players of all-time.