The Challenger-class cruisers were a pair of second-class protected cruisers built for the Royal Navy in the first decade of the 20th century. One ship, HMS Encounter, was later transferred to the Royal Australian Navy.

Protected cruisers, a type of cruising warship of the late-19th century, gained their description because an armoured deck offered protection for vital machine-spaces from fragments caused by shells exploding above them. Protected cruisers resembled armored cruisers, which had in addition a belt of armour along the sides.