TMs (Technical Machines) teach your Pokémon new moves. Each TM can only be used once, so choose wisely! They are found throughout the region, given by NPCs, or purchased in stores. Examples include TM01 Focus Punch, TM13 Ice Beam, and TM26 Earthquake. HMs (Hidden Machines) also teach moves, but unlike TMs, they can be used infinitely and are required to progress through the game by interacting with the environment (e.g., Cut, Surf, Fly, Strength, Rock Smash, Waterfall, Dive). HMs cannot be forgotten without the help of the Move Deleter in Lilycove City. Ensure you have Pokémon capable of learning and using all necessary HMs to explore Hoenn fully.
While the core list remains consistent, Pokemon Emerald introduces the ability to rebattle Gym Leaders, making it easier to earn the money required for expensive technical machines.
While HMs in Ruby and Sapphire provide permanent field utility, Pokémon Ranger reimagines this environmental interaction through Field Moves used by temporary partner Pokémon.