I would like to bring these two charts to the attention of all current and former Pokémon fans:

A. The type matchup chart from Bulbapedia: B. The chart used on pokemondb.net: The matchups themselves are all accurate—what I'm interested in is the ordering of the types. I'll call the one found on Bulbapedia List A and the one found on Pokémon Database List B:

List A	List B
Normal	Normal
Fighting	Fire
Flying	Water
Poison	Electric
Ground	Grass
Rock	Ice
Bug	Fighting
Ghost	Poison
Steel	Ground
Fire	Flying
Water	Psychic
Grass	Bug
Electric	Rock
Psychic	Ghost
Ice	Dragon
Dragon	Dark
Dark	Steel
Fairy	Fairy

Why the difference? Is it just arbitrary how the types are ordered? Well, no, there is some logic to it, and there are a few in-game sources we can look to for a "canonical" ordering of the types. The first thing to notice is that List A is really two lists: The first nine types were all Physical types prior to Gen IV, while the last nine (aside from Fairy), were all Special. What this meant is that all moves of the first nine types would deal Physical damage, making calculations with the Attack and Defense stats, among other effects, while the others deal Special damage, using the Special Attack and Special Defense stats instead, though as of Gen IV, with the Physical/Special Split being introduced, the damage category of moves is independant of their type, meaning there's no real reason to categorize the types in this way in regard to the newer games. The Fairy type was added in Gen VI, so it was never categorized along these lines, but it still makes sense to treat it as a Special type due to Sylveon. Since all of the other Eevelutions had Special types, it would only make sense for Fairy to also be one, as well as ensuring that there's exactly nine of each category.

However, even if you sort the types in List B by category, there's still a few minor differences that make it a distinct order. So, where do they come from? Well, if you look into the games themselves, you'll find that there's not actually any complete list of the types visible while playing the Gen I games. Checking a decompiled version of the first three generations by github user pret, the Gen I games seem to store the types with the ordering of List A, though with Bird type included in the Physical list. This order was mostly preserved into the second generation, when a menu was added to the Pokédex to sort by type. However, this menu actually displayed the types in the order of List B, though with Grass and Electric swapped, making that the first ordering visible to players in game. Looking further into the Gen II games' code, List B (without Grass and Electric swapped) is used in the portion that encodes type effectiveness (in Gen I the encoding is more disordered), meaning there's actually three different orderings used in those games in some capacity. The earliest trace of it I could find of List B is this chart from a 1998 Red and Blue player's guide in Nintendo Power, meaning it predates the release of Pokémon Gold and Silver:

In later generations, the Pokédex consistently uses List A in its search feature, making Gen II unique, so presumably List A continued to be used as the way the games internally store the types even after the Physical/Special Split in Gen IV. However, list B does continue to appear in the games in menus relating to type matchups, such as in the Move Tester Pokétch App in the Gen IV games, and the matchup chart in the tutorial for the Gen VIII games:



Based on this, I'd wager that List A constitutes the standard ordering of the types programmatically. In other words, if we were to assign an ID number to each type, it would make the most sense to base that on List A. List B, on the other hand, seems to be the canonical ordering of the types in public media, particularly for type matchup charts, though there's some variation as to whether Electric or Grass comes first. The ordering of the starter types itself is interesting, as while these lists consistently order them Fire-Water-Grass, the Pokédex ID numbers of the starters has always ordered them Grass-Fire-Water. As far as I can tell, the Pokédex order seems to just be a result of what order the Gen I starters were designed in, with Bulbasaur coming first according to the internal ID numbers. Everywhere else, Fire-Water-Grass was used, such as in the professor's lab, where Charmander was found in the leftmost ball and Bulbasaur in the rightmost one. This was also the order in the lab in Gen II, but from Gen III onward, this was changed to Grass-Fire-Water.[1]Sorta, the later games tend to place them in a circle, so it's debatable which one if any is "first".


As a final exercise, I've come up with an original ordering of the types based on how late in the game you'll typically fight a boss who specializes in that type. In other words, what is the average rank of a Gym Leader or Elite Four Member who uses that type?

There's a lot of variation in how you could weigh the different gyms and elite four members, especially when it comes to Gen VII, but I like this ordering the best as it places Normal first like the others.