ROM hacks, also known as hack games or ROM spots , are video games that have been edited or altered by enthusiasts. The hackers accomplish it by altering the code of the Read-Only Memory of a printed video game to create something fresh.

The core string Pokémon game process is considered very versatile and lends itself well to adjustment, giving anglers a lot of creative freedom together with a solid, well-tested engine. These factors, as well as Pokémon's remarkable popularity around the world, has resulted in the development of tens of thousands of unique games spanning multiple generations, which range from minor alterations to additional new features and, more and more often, entirely new fan-made Pokémon games. Although the core-series is definitely the most popular string to hack, there are also many fan-created Pokémon games which don't use these as premise, and instead are, as an instance, modified versions of their Pokémon Mystery Dungeon collection along with Pokémon Conquest.

These are real copies of published games that are sold to consumers, frequently flashed onto after-market game paks or game cards and lacking the official Nintendo Seal. But as ROM hacks are often dispersed across the Internet at no cost, they are regularly marketed as bootleg games, generally against the user's wishes. The reliability of those bootlegs are often inferior, and is now such a problem that hackers have begun to introduce warning displays in their games, even cautioning investors who when they paid for it, they Additional reading may have been scammed.

Early Pokémon ROM hacks date back to the late 1990s with altered variants of Pokémon Red. These were frequently relatively minor alterations like sprite or dialog changes, and could normally follow the flow of the first game. These early ROM hacks were infamous for being particularly primitive in nature, ranging from swapping Pokémon and individual sprites round to replacing the dialogue with disgusting text.

This trend continued until the release of Pokémon Brown by user Koolboyman from the early 2000s, among the most notable Pokémon hacks ever. This is the first hack to completely re-invent the game, with a brand new area and completely new storyline. Later editions included an enlarged Pokédex (including Pokémon from Generations II, III and IV), added dungeons and extra plot tweaks. It is but one of the very few completed hack games and has been successful enough to warrant a sequel (Pokémon Prism, that a Pokémon Crystal-based hack) and a Generation III version (Pokémon rijonAdventures) according to Pokémon FireRed.

Since Brown, Pokémon hacking's notoriety has expanded exponentially, with programmers creating many applications tools for desktop operating systems to help make maps, edit sprites, graphics as well as developing scripting languages especially for the Pokémon match engine. In addition, it has inspired many hackers to learn to edit the matches' gathering code right (known as ASM hacking). Various hacks have been released, frequently using FireRed as a foundation, for example Pokémon ShinyGold, Pokémon Naranja and also the Pokémon Ruby Destiny series, merely to name a couple.

There are numerous sites dedicated to Pokémon ROM hack development. Notable examples include Skeetendo, PHO and PokéCommunity's ROM Hack section, the largest known English-language Pokémon ROM hacking network. Many of these sites hold award nominations and services to showcase a few of the best gifts of the community.