Since 1950s unstable homotopy decomposition has been a fundamental subject in homotopy theory. It serves as a basic natural way to understand homotopy properties, for instance various global characterizations of homotopy groups. In this talk, I will give an overview of the development of this topic based on our recent comprehensive book “Unstable Homotopy Decompositions” joint with Stephen Theriault, including various decomposition methods, some major applications and several open problems.