This work is an attempt to restore volition as a respectable topic for scientific studies. Volition, traditionally conceived as the act of will, has been largely neglected in contemporary science and philosophy. This book develops a volitional theory of action by elaborating a unifying conception of volition, where volitions are construed as special kinds of mental action by which an agent consciously and actively bridge the gaps between deliberation, decision and intentional action. Volition can be a suitable object of empirical studies, and can be substantially demystified by exploring when and where volitions occur in the brain. The classical notion of volition as action initiator, which is essential to the commonsense image of human agency that underlies our ordinary understanding of free will, moral responsibility and human dignity, can be preserved in face of the challenge from recent experimental studies in neuroscience, such as Benjamin Libet's famous experiment. This work will be of interest to philosophers of mind and action, psychologists and cognitive neuroscientists, as well as general readers who are interested in understanding the nature of human mind and agency.