There are many works on this topic, from the fields of spirituality, psychology, anthropology, philosophy, medicine, history, and literature. The few books and authors listed here are offered for those who may want basic information about core shamanism, Celtic shamanism, shamanic aspects of process-oriented psychology, soul retrieval, and Toltec energetic practices.
Michael Harner The Way of the Shaman
Sandra Ingerman Soul Retrieval: Mending the Fragmented Self
Caitlin Matthews Singing the Soul Back Home
Arnold Mindell The Shaman's Body
Merilyn Tunneshende Twilight Language of the Nagual