While playing , you'll naturally uncover new codex entries by examining various things in your surroundings and speaking with your squadmates and other NPCs. Exhausting all dialog options with characters and talking about their history and families is a great way to uncover more codex entries.
In Mass Effect and Mass Effect Legendary Edition, there is an achievement/trophy (Scholar for the original and Archivist for the Legendary Edition) for obtaining all primary alien codex entries. This can be harder to obtain than you might think as one of them appears to be missable, which can potentially lock you out of this accolade if you don't get it. Just below we have a full guide on where to get each codex. You can check your Journal to see which codex entries you have already obtained via the menu.
All Primary Alien Codex Entry Locations
Council Races
- Turian: Automatically obtained after speaking with Nihlus at the beginning of the game.
- Asari: Automatically obtained after your first meeting with the council near the beginning of the game.
- Salarian: Automatically obtained after your first meeting with the council near the beginning of the game.
Extinct Races
- Prothean: Before you head to Eden Prime, speak to Captain Anderson and exhaust all dialog options to learn about the Protheans. (This is when you go to the Comms Room and have a meeting with Captain Anderson and Nihlus.)
- Rachni: Speak to the Avina VI near the Finacial District fast travel point to learn about the Krogan statue behind her and the Rachni War.
Non-Council Races
- Geth: When you meet Ashley on Eden Prime, exhaust all dialog options to learn more about the Geth.
- Batarian: Before you leave the Citadel, speak to Captain Anderson and exhaust all dialog options to learn about the Batarians. Alternatively, during the Bring Down the Sky mission, you can learn about them then too.
- Quarian: Automatically obtained when you recruit Tali.
- Krogan: Automatically obtained when you recruit Wrex.
- Keepers: Speak to the Avina VI near the Wards Access fast travel point to learn about the Keeper just beside her.
- Elcor: Speak to the Elcor diplomat in the room beside the Human Embassy and exhaust his dialog options to learn more about the Elcor.
- Volus: Speak to the Volus diplomat in the room beside the Human Embassy and exhaust his dialog options to learn more about the Volus.
- Hanar: In the Citadel, speak to the Hanar merchant or the Preaching Hanar near the Wards Access fast travel point and exhaust all dialog options to learn more about the Hanar.
Once you have collected all of the codexes, your Scholar or Archivist achievement/trophy will pop. Don't forget you can check in your journal to see which you are missing.