In spite of considerable efforts over the years to understand and combat materials degradation via corrosion processes, many challenges still remain both in the theoretical understanding of the phenomena and in seeking pratical solutions to the perennial problem. Progress has been slow due to the complexity of the processes and the systems involved. Fortunately, in recent years there has been a renaissance in the development of new electrochemical and optical techniques, as well as advances in instrumentation, which have greatly aided our quest to gain insight into the complex mechanisms involved in metallic corrosion and passivation. Numerous scientific meetings, symposia, and workshops have been held allover the world which attest to the frenzy of activities in corrosion science and technology. However, most of these conferences have dealt mainly with recent research results. There appeared to be a need to assess and disseminate our present state of knowledge in the field as regards measurement techniques, theory, and instrumentation. The present NATO Advanced Study Institute was therefore held in Viana do Castelo, Portugal from July 9 to 21, 1989. The Institute consisted of a series of tutorial lectures, poster sessions, and round-table discussions interspersed evenly over the two-week period. It was attended by 75 participants from several countries representing industry, government and university laboratories.