Taking into account modern scientific views on the content and structure of scientific theory, the monograph presents a criminalistic theory of situations. The main content of the criminalistic situation is reflected: its subject and object, method, tasks are defined, the basic principles of the situational approach are formulated. A classification scheme of criminal, investigative, operational-search, expert and judicial situations that are the objects of forensic research has been developed . The problems of situational approach to the analysis of criminal event and criminalistic activity. A methodology for modeling investigative situations has been developed, modeling capabilities are shown as a means of optimizing investigative decision-making. The proposed method of situational modeling is intended for the investigator’s practical work (mental analysis of investigative situations, reconstruction of criminal situations, modeling of tactical decisions of the criminal, making his own tactical decisions). The book is addressed to students, graduate students, teachers of criminology, as well as law enforcement officers