Self-orientation in space is based on multisensory interactions of visual, vestibular and somatosensory-proprioceptive signals. In this article, we analyze vestibular signal processing in terms of its capacity to provide inertial cues for self-orientation in space. We show that vestibular signals from both the otolith organs and the semicircular canals must be processed in a bootstrap-operation like manner in order to obtain true inertial head-in-space orientation.