Are US and European versions of GBA games compatible?

[fatbatch]

I have Pokemon Saphire (US version) and am looking to get Pokemon Ruby for my son - do I need to get the US version to be able to trade, battle etc?

[Mayhem]

Probably. I have heard Pokemon titles of different regions can talk to each other, but in general on the GBA, different regions DO NOT talk to each other.

[Greng]

When the system 1st came out I remember there where issues with either F-Zero, or Mario Kart. Sometimes US>JP will be fine but US>EUR wouldn't work. Basically, it's not guaranteed which regions of games are compatible with each other.