Abstract: Transmission electron microscopy (TEM) has been one of the most important analysis techniques to visualize the microstructure of materials in a direct way. In the course of almost a hundred years of progress, the birth of aberration-corrected TEM (AC-TEM) has been the most recent revolutionary development, and has been essential for the advancement of materials science in the past decades. In this article, we review the principle, advantages, applications and developments of AC-TEM through three questions:“What is AC-TEM?”,“How is AC-TEM advan‐tageous?”,“What else can AC-TEM do more than acquiring atomic-resolution images?”.