Investigation is used for actively searching, looking for clues, gathering information, experimentation, and research. The most commonly used ability score is Intelligence. Examples include the following activities:
| DC | Activity |
| 10 | Notice an old and frequently-used secret door; find out what inn someone’s staying at |
| 15 | Discern simple truths from a crime scene; find a specific passage in a daunting tome |
| 18 | Identify patterns of thieves’ cant in a town; determine how long ago a recent event took place |
| 20 | Get dangerous gossip on a well-known local; assemble a timeline of suspicious happenings going back as far as 6 months |