The TANDEM project is targeting the Marie Sklodowska-Curie Doctoral Networks / Joint Doctorates 2023 call for proposals, with the objective of recruiting and training 15 Doctoral Candidates (DC) and awarding them with joint doctoral degrees from two of the network partners. Microelectromechanical systems (MEMS) are some of the key enabling technologies of the 21st century, as they are now the core components of a wide range of technical systems ranging from daily consumer products like smartphones to biomedical applications and the space industry. Yet, in order to handle, manipulate and control ultra-small volumes of fluid with high precision, advanced MEMS devices still need to be developed, as many of the phenomena on the macroscopic length scales do not apply on the microscopic length scales of microfluidic devices. This is why the TANDEM project aims to address engineering thermodynamics issues directly linked to miniaturisation in order to develop innovative and complex microsystems with applications in the fields of health, energy and environment. The development of these new microsystems is in the continuity of the research activities developed in 2 former ITN projects MIGRATE and GASMEMS, in which real advances have been made in understanding gas flows with heat transfer in MEMS, mainly with fundamental knowledge, and first steps have been taken towards miniaturised applications. The scientific objective of TANDEM is now to improve knowledge on fluid and heat transport in the specific context of mechanical, biological and chemical engineering thermodynamics. The aim is to design a new generation of complex microsystems and demonstrate that they are working, thus integrating the previous bricks and new ones together in given applications to develop demonstrators in the lab and relevant environment (TRL4-5). To achieve this objective, experimental and numerical studies will be conducted to solve flow and heat transfer problems in the context of these complex microsystems, yet many different challenges, identified from the state-of-the-art analysis, need to be addressed. In particular, the high scientific and technological potential of thermal machines at the microscale is currently underexploited in Europe, essentially due to a compartmentalisation of skills. The main goal of the TANDEM network is to overcome these barriers and reinforce collaborations and dialogue by elaborating a common language, through each step from the scientific fundamentals to applications. The different teams involved in the TANDEM consortium have developed an expertise in various disciplines and some of them have already collaborated in GASMEMS and MIGRATE or in other bilateral research projects. Interdisciplinarity will be at the core of the TANDEM project through the co-supervision of all the PhD students, and the overall organisation of the TANDEM project will reinforce this interdisciplinary work. The objective is to propose a new and innovative doctoral programme not yet correctly covered by the existing doctoral schools/programmes in Europe. A new generation of microsystems will be designed based on innovative technologies involving physical phenomena at microscale, which have so far been poorly implemented, and will tackle the current constraints of low cost, transportability, and low energy consumption. Special attention will be paid to the sustainability and circularity of the process. Given the urgency of the current health, energy and climate crises, the TANDEM project and consortium have the ability to provide concrete tools and solutions to today’s critical societal challenges.