The endTB (Expand New Drug Markets for TB) consortium consists of three NGOs: Partners In Health (PIH), Médecins Sans Frontières (MSF) and Interactive Research and Development (IRD). Funded by Unitaid, the objective of endTB is to promote better and safer MDR-TB treatment regimens. The endTB Observational Study currently has sites in 17 countries. In each country, sites enroll patients on treatment with bedaquiline and delamanid according to National TB Program guidelines, while collecting clinical and bacteriological data related to efficacy and safety. This Technical Basis document provides the rationale for clinical decision-making, screening tools and data definitions that are used at the endTB Observational Study sites. This is a living document. If you would like to suggest an additional topic, please email us at endTB1@pih.org.