Electron’s unique characteristics allow itself to be used as an extremely useful probe of atomic-scale structural details of the ultrasmall world. More scientific questions can be answered if we are able to see how the atoms move in real-time instead of only static images. This challenge requires generating, controlling and measuring electron beams with unprecedented brightness at picosecond or better temporal precision, which become possible only very recently building on the tremendous progresses on ultrafast lasers and particle accelerators. In this talk, I’d like to share with you the history and new development of this exciting research area. A particular focus will be given to a new trend – the use of a few mega-electron-volt high energy electrons – a most promising route toward shorter and brighter beams. R&D in this new direction is pushing forward the research frontiers in particle accelerators and beams, and will also greatly benefit studies in condensed matter physics, biology, chemistry, and materials science.