This Special Issue will publish selected papers from the International Symposium on Thermal Effects in Gas flow in Microscale ISTEGIM 2019 - A MIGRATE Event (http://www.istegim.eu/), 24-25 October 2019, Ettlingen, Germany. MIGRATE (www.migrate2015.eu) is a H2020 Marie Skłodowska-Curie European Training Network, intended to address some of the current challenges to innovation that faces European industry with regard to heat and mass transfer in gas-based micro-scale processes. This network of 10 participants and 6 associated partners coming from all over the European Community covers different aspects of enhanced heat transfer and thermal effects in gases: from modelling of heat transfer processes and devices, development and characterization of sensors and measurement systems for heat transfer in gas flows as well as thermally driven micro gas separators, to micro-scale devices for enhanced and efficient heat recovery in environmental, transport, telecommunications and energy generation. The MIGRATE Project presents his 2-day symposium, ISTEGIM19, during which the members of the MIGRATE network will showcase the main achievements of the project. The program will include keynote lectures, invited lectures and contributed papers.