Each item has an index number that identifies it in any game. The following list enumerates them according to the way they are stored in the Generation IVNintendo DS games.
Before Generation IV, the index number for a given item is not consistent between generations. For example, the Moon Stone in Generation III is index 94, but in Generation IV it is index 81. In games after Generation IV, items may be added (or occasionally updated), but they are not removed. Moon Stone is index 81 in all games since Pokémon Diamond and Pearl.
List
Rows highlighted in gray indicate items introduced in Pokémon Platinum; rows highlighted in gold were introduced in Pokémon HeartGold and SoulSilver (or exclusive if next to a row with the same index); and rows highlighted in blue are exclusive to Diamond, Pearl, and Platinum.
There are some items which are not available during normal gameplay, such as region-exclusive items or items which have no actual purpose in the final releases. The only way to get these items, other than the Seal Bag, is through cheating.
While the blank items in the middle of the list can be displayed, the "items" after the last item in the list cannot. The list can be viewed in-game if such item exists in the save file, but these items are unnamed and the game crashes when selected. If these items are given to Pokémon and put on the GTS, then they will crash the game if that Pokémon is selected.
This article is part of both Project ItemDex and Project Games, Bulbapedia projects that, together, aim to write comprehensive articles on the items in the Pokémon world and the Pokémon games, respectively.