The Body Keeps the Score by Bessel van der Kolk
One of the most widely recommended books on how trauma affects the mind and body.
What Happened to You? by Oprah Winfrey and Bruce D. Perry
A compassionate shift from asking "What's wrong with you?" to "What happened to you?"
Healing the Fragmented Selves of Trauma Survivors by Janina Fisher
Especially valuable for understanding trauma responses and parts work.