This boo firstly presents the definition of polar low,and then reviews the history of polar low study.The general features of polar lows over the Japan Sea and the neighboring Northwestern Pacific are systematically summarized based on the author's previous researches.Three polar low cases over the Japan Sea that occurred in February 1996,January 1997 and February 1997 are focused on,respectively.The observational features and evolutionary processes of these polar low cases are described in great detail.Moreover,their developments are simulated well by using JSM,RSM and MRI-NHM,respectively.Also emphasized are the discussions of the development mechanism of these polar lows.This is an reference handbook for the researchers and postgraduate students in the fields of atmospheric and marine sciences as well as mathematics and fluid dynamics.