# Where do the rules say a thief or bard can gain two-weapon fighting proficiency?

I heard several times that thieves and bards can be proficient in two-weapon fighting, but I don't see that anywhere in the Player's Handbook. In fact, I don't even see two-weapon fighting mentioned as a proficiency. I'm just starting to fully grasp the AD&D2E rules, so I'm oftentimes not sure where to look for specific rules.