Traffic engineering of ISDN has become a key area of CCITT Recommendations since 1985. This paper reports on the first recommendations formalized in a dedicated series on ISDN traffic engineering, the CCITT E.700 series of Recommendations. It also reports on the ongoing work towards an extension of the series so as to cover integration of mobile services into ISDN, the E.750 series, and reviews future directions related to such emerging issues as intelligent network services, and B-ISDN/ATM.