This International Standard specifies the requirements for the performance of speech communication for verbal alert and danger signals, information messages, and speech communication in general. Methods to predict and to assess the subjective and objective performance in practical applications are described and examples are given. In order to obtain optimal performance in a specific application, three stages can be considered: a) specification of the application and definition of the corresponding performance criteria; b) design of a communication system and prediction of the performance; c) assessment of the performance for in situ conditions. The use of auditory warning signals other than speech is not included in this International Standard but is covered by ISO 7731.