Tunnel boring machines (TBM) are increasingly used for tunnelling with difficult and complex geological conditions, including rock and soil mixed and interfaced grounds, spalling and bursting rocks, squeezing and swelling grounds, blocky and highly fractured rocks, fault and shear zones, and grounds under high in situ stress and water pressure. Improvement and optimisation of TBM’s performance in those difficult ground conditions require good scientific understanding, innovative technology development and good engineering practice, that involve tunnelling and geotechnical engineers, designers and contractors, TBM manufacturers and material suppliers, and researchers. The tunnelling industry has been facing the challenges of TBM in difficult and complex geological conditions and working together to find solutions. For examples, the International Tunnelling and Underground Space Association (ITA) has a Working Group on “Mechanised Tunnelling”, the European Commission sponsored R&D projects on “Technology Innovation in Underground Construction“ (Framework Program 6) and “New Technologies for Tunnelling and Underground Works“ (Framework Program 7). In China, a number of national key laboratories on TBM technologies have been established in the recent years. TBM DiGs (Tunnel Boring Machines in Difficult Grounds) is planned to be an international conference series to provide a specialised technological forum discussing and exchanging knowledge related to TBM works in difficult grounds. The conference plans to cover a wide range including characterisation of difficult grounds, field observations and case studies, physical and laboratory tests, numerical modelling and techniques, treatments of difficult grounds, TBM design and installation, tunnel support design, monitoring and risk management. TBM DiGs 2015 is to be held in Singapore, jointly organised by the universities and supported by the tunnelling community worldwide, interested in TBM tunnelling technologies. The Organisers would like to welcome researchers and practitioners involved with TBM tunnelling to the TBM DiGs 2015 conference to share, to cooperate, and to progress.