This paper presents the summarized information on the mechanisms of neuroimmunoendocrine organism reaction to external adverse impacts (irrespective of their etymology), and on the key elements in these reactions development. It is found that adverse external factors are responsible for a change of an organisms functional state, involving neuroendocrinal and immune systems in the (stress) reaction formation. Neuroendocrinal and immune systems act like coordinators of the intersystemic and interorgan relations in the setting of both adaptive and pathological processes. The combination of feed-forward and feedback (positive and negative) connections controlled by hormones, neuromediators, neuropeptides, cytokines and their corresponding receptors, serves as the basis of neuroendocrinal and immune systems interaction. Through mediators and hormones, the neuroendocrinal system modulates the immune system, and the latter can modulate functions of the former due to its cytokine network. Along with humoral mechanisms, the vagal nerve which enables the reflectory control of immunity, is the key component of the system providing the functional unity of nervous and immune system. The conversion of immune signals to neural ones is done through activation of vagal afferent fibers by proinflammatory cytokines, whereas its efferent fibers, forming the cholinergic anti-inflammatory pathway, ensure the descending central nervous system effects which prevent the hyperactivation of innate and adaptive immune reactions. The body balance control is based on the integrative activity of nervous, endocrinal and immune systems both under normal and pathological conditions (traumas, infections, stress, physical and chemical exposures, etc). The systematization of information about the coordinated neuroimmunoendocrine interaction provides background for theoretical underpinning of the upcoming trends in search of means and ways to correct the negative influence of adverse external factors on a living organism.