We have heard a lot about the exciting new materials being used in microelectronics, and I would like to describe some experiments making use of in situ electron microscopy to try to understand the mechanisms of the reactions that these materials undergo during deposition and processing. I will discuss experiments in which we carry out one of these reactions within an electron microscope and record the effect on the specimen in real time. We then use measurements from the recordings to analyze the reaction mechanism in a quantitative way. In this article, I will cover two types of experiments. First, I will describe experiments in which we examine the motion of surface and interface steps during reactions, and I will discuss how that information allows us to determine reaction mechanisms. In this context, I will consider silicon oxidation and silicide formation. In the second type of experiment, we look at how surface morphology changes during reactions. In particular, we will try to understand the growth mechanism of “quantum dots,” which are becoming important for some novel microelectronic applications. After discussing these results, I will describe our attempts to extend the technique of in situ electron microscopy to look at systems other than the solid—solid or gas—solid interface.