This book constitutes the proceedings of the 4th International Workshop on Symbiotic Interaction, Symbiotic 2015, held in Berlin, Germany, in October 2015. The 11 full papers and 8 short papers presented in this volume were carefully reviewed and selected from 23 submissions. The papers present an overview of the symbiotic relationships between humans and computers as well as novel advancements. The idea of symbiotic systems put forward in this workshop capitalises on the computers’ ability to implicitly detect the users goals and psycho-physiological states and thereby enhancing human-computer interaction (HCI). A special focus of this year’s Symbiotic Workshop will be on physiological computing approaches, e.g. using brain-computer interface (BCI) technology.