Electrical properties provide a window on processes that are of great interest in understanding Earth. Electromagnetic induction, which can image electrical properties, has undergone a major revolution in the last decade. The EMSLAB experiment, the largest electromagnetic induction study to date, has been a significant factor in this revolution. It has substantially advanced data processing and interpretation of electromagnetic induction data. It has also imaged conductive structure associated with subduction, volcanism, and continental accretion that provide important constraints on the role of fluids in these processes. Finally, EMSLAB has made significant contributions to the use of electromagnetic methods in physical oceanography. We outline the rationale and history of EMSLAB and briefly review the contributions of each the papers in this special section in the overall context. In particular, we compare and constrast the implications of papers interpreting a densely sampled central transect from the Juan de Fuca Ridge to eastern Oregon. ¿ American Geophysical Union 1989