The author presents an introduction to the concept of unconscious alliances, based on group therapies and group observations. Unconcious alliances, are psychic intersubjective entities constituted by subjects of a link or a community (unity) - a group, family, couple or an institute. Their aim is to strengthen certain processes, certain functions and certain structures. He distinguishes between structurant, defensive, offensive and pathogenic unconscious alliances. These alliances stay unconscious because of their functions and so do the psychic material that generates the links. The unconscious alliances have a metapsychological function; they enframe the psychic life, they contribute to its narcissistic and object organisation, to the ways in which the wish is fulfilled, and they support the psychic structuring in case of defensive or pathogenic compositions; they participate in the formation of the subject's unconcious.