Ratchet & Clank: Size Matters is a platformer/shooter in the Ratchet & Clank series developed for the Sony PlayStation 2. It was developed by High Impact Games, a company spawning from the original Ratchet & Clank developer, Insomniac Games. The story involves Ratchet and Clank as they are interrupted from their vacation to search for a kidnapped girl and encounter a forgotten race known as the Technomites.

As with previous Ratchet & Clank games, most of the game takes place controlling Ratchet on foot carrying a hand-held weapon, with Clank attached to Ratchet's back, functioning as a heli-pack. There are also sections of the game in which Clank is playable. He can solve puzzles with Gadgebots-small robots that do his bidding-to control, fight in space as Giant Clank in shooter-like mini-games, and participate in three different types of Clank Challenges: Demolition Derby, Gadgebot Toss (somewhat similar to basketball) and Gadgebot Survival (similar to Lemmings).

Ratchet can collect several pieces of armor in this game, one each for his head, torso, hands and feet. Seven distinct themed armor sets exist, all of which give unique abilities to his Omniwrench 10,000. Two of the armor sets can only be obtained by playing through Challenge Mode, one set for the first time through and another for the second. The pieces do not need to be worn as themed sets, however; they can be mixed and matched to form hybrid armor sets which provide him more damage protection and offer other abilities.