Abstract: As an important branch of physics, the study of thermotics boasts a long and illustrious history. Despite the increasingly sophisticated understanding of the nature of heat, significant challenges persist in heat flow manipulation, making it difficult to meet the ever-growing demands for thermal management amidst the current energy crisis. In 2008, the advent of steady-state thermal cloaking based on transformation thermotics ushered in a new research field—thermal metamaterials, offering a novel approach to address this challenge. Seventeen years of vigorous development has witnessed fruitful results, which will be delineated in this article. Starting from initial studies on thermal cloaking, topics have gradually expanded to include diverse functionalities such as thermal concentrators, thermal camouflage, and thermal illusions. Now, transitioning from pure heat flow manipulation to the realization of rich physical effects such as topological states of matter, research has extended from purely conductive heat transfer systems to composite systems encompassing convective and radiative heat transfer, successively achieving exotic physical effects such as non-reciprocity and non-Hermiticity, and giving rise to important applications such as daytime radiative cooling. As a new blossom on the “old tree”of thermotics, thermal metamaterials not only demonstrate unique merit in basic research but also provide innovative solutions to practical engineering problems.