Abstract: Polar sea ice is essential to the Earth system, functioning both as an indicator and an amplifier of climatic and environmental changes. In the context of global warming, Arctic sea ice has been declining during the past 46 years, yet Antarctic sea ice increased first before it significantly declined. Currently, sea ice in the two polar regions has reached unprecedented low levels. Changes in polar sea ice are associated with anthropogenic global warming and internal climate variabilities. Over the past four decades, researchers have obtained abundant findings about polar sea ice changes and potential processes by integrating field observations, satellite remote sensing, reanalysis data, and numerical simulations. Nonetheless, various factors responsible for the rapid changes in sea ice and their individual contributions remain inadequately comprehended. This study summarizes the characteristics of Arctic and Antarctic sea ice changes observed in recent decades and projections of future changes. It systematically elucidates the progress and challenges in the study of rapid changes in Arctic and Antarctic sea ice and mechanisms behind these changes from perspectives of interaction and feedback processes between the polar atmosphere and ocean, principal climate modes in the mid- and high-latitudes, and tropical-polar teleconnections, and outlines possible impacts of polar sea ice changes on both regional and global climate.