This issue of Microscopy and Microanalysis contains invited and contributed papers from the 1998 Arizona State University (ASU) Workshop on In Situ Electron Microscopy, held January 7-10 at the Embassy Suites in Scottsdale, Arizona. This was the eighteenth in a series of Workshops organized annually by the Facility for High Resolution Electron Microscopy in the Center for Solid State Science at ASU. The Workshops are part of an educational program, and are intended to foster interaction and collaboration between researchers in electron microscopy. The workshop was attended by over 80 participants from universities, industries, and government laboratories around the world. Many of the contributions to the workshop are included in this issue.