Skinchangers is a sourcebook for the Chronicles of Darkness. It presents Skinthieves, people who achieve animal transformation through unusual means.

Summary
From the Onyx Path catalog:

"Ahahaha! You, too? I knew I wasn’t alone!Oh, look at you — you’re magnificent.Where did you get those wolf pelts?Mine isn’t nearly as pretty, and I couldn’t find a wolf, but look! Let me show you!"— Fred Gahagan, SkinthiefThis book includes:

A detailed look at the skinthieves who achieve animal transformation on their own, including rules for player creation
The traditions and powers of those skinchangers born from spirit possession
A selection of unique skinchangers and strange origins, as well as collected animal lore to help Storytellers customize their own shifters