Thermal field theory is the study of quantum field theory at non-zero temperature. This proceedings introduces both retrospect and prospect for various aspects of thermal field theory as well as their extensive applications to condensed matter physics, high energy physics, cosmology, nuclear physics, etc. Also included are speeches memorizing the recently lamented Professor Hiroomi Umezawa, a leading physicist in thermal field theory, by his former students and colleagues.

Thermal field theory is the study of quantum field theory at non-zero temperature. This proceedings introduces both retrospect and prospect for various aspects of thermal field theory as well as their extensive applications to condensed matter physics, high energy physics, cosmology, nuclear physics, etc. Also included are speeches memorizing the recently lamented Professor Hiroomi Umezawa, a leading physicist in thermal field theory, by his former students and colleagues.