Low-energy electron microscopy (LEEM) is a relatively new microscopy techni
que, capable of high-resolution (5 nm) video-rate imaging of surfaces and i
nterfaces. This opens up the possibility of studying dynamic processes at s
urfaces, such as thin-film growth, strain relief, etching and adsorption, a
nd phase transitions in real time, in situ, as they occur. The resulting vi
deo movies contain an unprecedented amount of information that is amenable
to detailed, quantitative analysis. In this paper we discuss the principles
of LEEM and its application to problems in science and technology.