Since 2002, STIB has committed to a quality certification process for its services under NF Service standards (NF 281 – EN 13816 certification). In 2014, for the first time, 100% of the network was "service quality" certified by the independent French body AFNOR Certification. These certifications are the result of objective assessments of the quality of the services offered to passengers, whether in terms of punctuality, cleanliness, the attitude of staff or passenger information.

Since May 2019, following an update to the standard, STIB has received a unique "Quality of Service for passenger transport" or NF Service certification for the services offered to passengers and identified in the framework of the standard.

A committee of representatives from STIB, the Region and customers meets every year to develop a set of service commitments. Most of the measurements are made by "mystery shoppers". Others are calculated automatically by IT systems.

The certificate is valid for 3 years, and every year STIB must demonstrate that the annual results of the daily assessments by the mystery customers or IT systems reach the requirements or, where applicable, improvement plans are implemented to achieve them.