Active research in the development of hydrogen-fuelled low-emission engines is being pursued at the Engines and Unconventional Fuels Laboratory of the Indian Institute of Technology (IIT), for a period of close to two decades. This paper highlights the significant pursuits and attainments of the research and development (R&D) activities carried out in IIT, Delhi on hydrogen-operated engines. Both spark ignition (SI) and compression ignition engine test rigs have been developed and instrumented for the use of hydrogen fuel. Several existing petroleum-fuelled engine configurations have been modified by taking care to observe that the converted system does not need substantial hardware modifications. Various fuel induction techniques have been experimentally evaluated keeping in view the temperamental combustion characteristic of this fuel. Curative and preventive steps have been adopted and suitable retrofits and subsystems have been installed at the appropriate locations to preclude the possibility of any undesirable combustion phenomena such as backfire, knocking and rapid rate of pressure rise. Performance, emission and combustion characteristics of the systems have been determined. It has been observed that an appropriately designed timed manifold injection system can overcome the problem of backfire in a hydrogen engine. NOx emission level from a hydrogen-operated SI engine can be drastically reduced by way of lean engine operation. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.