Shadow work is a concept and practice that stems from the field of psychology. Carl Jung referred to the subconscious and the darker aspects of self that often hide there as the human “shadow”. When we work with our shadow as witches, we are blending our spiritual and magical practice with techniques for psychological self-exploration and self-improvement.
This is one aspect of magical practice that I see discussed frequently among rootworkers, ceremonial magicians, and traditional practitioners, but I rarely see it discussed in modern witchcraft texts. Part of the reason for this is that much of the readily available material for modern witches is quite beginner focused, finding material aimed at intermediate and advanced witchcraft is tough without getting into other branches of magic. This is no excuse though.
For every user of magic, beginner or otherwise, “Know Thyself” should be a primary focus of their practice.
The pursuit of self knowledge unlocks power that many people can only imagine. If you want to change your life (and that is the point of witchcraft, isn’t it?) then becoming very familiar with all parts of yourself will unlock your capacity to make radical, pervasive changes in your life. And for that, there's no better practice than Shadow Work.