General theory of diagnosis is applied to psychodiagnostics. Its specificity as recognition activities is shown, as well as its difference from other forms of psychological cognition (measurement, research). Position in scientific system and structure of psychodinamics are marked out. Psychodiagnostics is considered to be a division of practical psychology as well as psychoprognostics, psychocorrection, psychoprevention. Psychodiagnostics is formed out of four components: semiotic, technical, deontological and logical.