So I was inspired by another thread about special Leadership rules in 40k to get around to something I've been planning on doing, but haven't really gotten around to: compiling a list of the Psychology rules in 40k. Back in the day, starting with Rogue Trader, Warhammer 40,000, like Warhammer Fantasy Battle, had a list of psychology rules detailing how units could behave on the battlefield. Although a separate section of Psychology rules disappeared with the 3rd edition of 40k, the Psychology rules have simply migrated to other parts of the rulebook.
Gone to Ground (Pinned)
Stunned & Shaken (vehicles)
-Casualties from shooting
-Losing close combat
Army Specific Rules
Space Marine Psychology
And They Shall Know No Fear
God of War
Chapter/Company Banners (units within 12" re-roll Morale and Pinning tests)
Honour of the Chapter (Confers Fearless on unit IC joins)
The Power of the Machine Spirit
Don't Press Dat
One Scapel Short of a Medpack (Confers Fearless on unit IC joins, gives Rage, limits leaving unit)
More to come...