The article reviews the issues of compatibility in different scientific and technical fields. Together with its definitions and criteria, principles and forms of its application are described. The list of requirements to companies’ members before starting relationships and during their cooperation is suggested for quality evaluation of parties' cooperation. The option of functional preparedness is suggested, i.e. state of the system's compatibility before starting cooperation with another system being a participant of the events. The use of certain asymptotics is suggested for evaluation of the cooperation effectiveness.