The IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm) was held at the Cosmopolitan Hotel and Casino in Las Vegas, NV from May 28 – May 31, 2019. This was the 31st Anniversary of ITherm, first held in 1988. The conference was historically held every other year until 2016 when it switched to an annual schedule, making this the 18th ITherm. ITherm 2019 was sponsored by the IEEE Electronics Packaging Society (EPS) and co-located with the 69th Electronic Components and Technology Conference (ECTC 2019). ITherm is also an IEEE EPS partner conference of the International Workshop on Thermal Investigations of ICs and Systems (THERMINIC) in Europe and the Electronics Packaging Technology Conference (EPTC) in Asia.