This Recommendation provides an overview of the ITU-T Q.95x-series of Recommendations on the Stage 3 descriptions of ISDN Supplementary Services and the general principles on which these Stage 3 descriptions are based. The ITU-T Q.95x-series of Recommendations is structured and numbered in a similar manner to the ITU-T I.25x-series of Recommendations on Stage 1 ISDN supplementary services descriptions and the ITU-T Q.8x-series of Recommendations on Stage 2 descriptions. The ITU-T Q.95x-series of Recommendations cover the protocol descriptions for DSS1. An overview of the SS No. 7 protocol descriptions is provided in ITU-T Q.730 [1]. The Stage 3 protocol descriptions in the ITU-T Q.95x-series using the Facility Information Element of the Functional Protocol are based on the generic procedures established in ITU-T Q.932 [5]. Any of the generic procedures in ITU-T Q.932 [5] (Keypad, Feature Key Management and Functional Protocols) can be used for the control of supplementary services. The detailed functional protocol procedures are provided in the ITU-T Q.95x-series Recommendations. This Recommendation lists the allocated INTEGER values for operations and errors defined in ITU-T Q.932 [5] and for supplementary services defined within the ITU-T Q.95x-seriesRecommendations. The individual ERROR values are complemented by a brief definition of the error characteristics.