The “sacred plants", which are often called hallucinogens and psychedelics, have played important roles in ancient and contemporary societies, evoking powerful spiritual, emotional, social and cognitive reactions. Their importance for humanity is attested to by findings in many areas: ethnographic research on the cross- cultural patterns of use; clinical observations of their therapeutic effects and properties; neurophysiological laboratory studies on their roles as neurotransmittors; and consciousness studies and theory. Cross-cultural studies of traditions utilizing these substances as therapies, and neurobiological research on their mechanisms of action, have advanced considerably in the last decades. Integration of this research on their effects from biophysiological through psychocultural and cognitive levels has contributed to the development of new perspectives. This neurophenomenological approach suggest that these substances be referred to as “psychointegrators" (from psyche, meaning mind, soul and spirit), based upon their common neurophysiological and experiential properties. Their importance lies in the activation of emotional and personal processes of the limbic system and paleomammalian brain which underlie personal identity, attachment and social bonding, emotional stability, convictions and beliefs, and their integration with neocortex processes. Psychointegrators stimulate the integration of behavioral protomentation and social—emotional dynamics with language based ratiomentation, egoic representations and personal identity. These biochemically based physiological effects may force: emotional reactions, awareness of repressed memories, integration of emotional and rational processes. and the resolution of conflicts through integration of different functional systems of the brain. This volume provides a broad overview of psychointegrators and the bases for their constructive utilizations. The first section provides a theoretical framework for understanding the importance and significance of these psychointegrators. The second section covers clinical and social perspectives on their uses and effects. particularly as studied within Western biomedicine. The third section provides ethnographic examples of contemporary traditions which attest to the positive roles and functions psychointegrators can play in human societies. This introduction provides a neurophenomenological framework for assessing these substances.