SegaDevs

Sega Development Studios
Japan AM; 1990 - 1998-ish
Sega AM1 \| Sega AM2 \| Sega AM3 \| Sega AM4 \| Sega AM5 \| Sega AM6 \| Sega AM7 \| Sonic Team
Japan AM; 1998-ish - 2004-ish
WOW Entertainment \| Sega AM2 \| Hitmaker \| Amusement Vision \| Sega Rosso \| Smilebit \| Overworks \| Sonic Team \| United Game Artists
Japan; 2004 onwards(?)
Sega WOW \| Sega AM2 \| Sonic Team \| Sega Sports Design \| Ryu ga Gotoku Studio \| AM Ishoku Team
Japan non-AM, demerged, and defunct
Puyo Puyo Sega \| Sega Networks \| ??? Demerged: Sonic! Software Planning \| Nextech \| SIMS \| ??? Defunct: Esco Boueki \| Megasoft \| ??? Miscellaneous: Sega Toys? considered a separate company from the main Sega \| CRI? did they develop anything between them being bought by Sega and being merged into AM2?
North America
Three Rings Design \| ??? Defunct: Sega Electronics \| Sega Technical Institute \| Sega Midwest Studio \| Sega Interactive \| SegaSoft \| Sonic Team USA/Sega Studios USA \| ???
Europe
The Creative Assembly \| Sports Interactive \| Hardlight Defunct: Sega Racing Studio
Others
Sega (Shanghai) Software \| Sega Studio China
Unknown Location
Sega Away Team

Rough idea of what's going on - fix it plz

From Sega Retro