The fourth in a series of NASA-AEC Liquid-Metals Corrosion Meeting held October 2-3, 1963, was devoted to discussion of the mechanisms of liquid-metal corrosion, the results of compatibility tests with alkali metals, and the problems related to compatibility testing with alkali metals. Previous meetings in this series dealt with a broader range of topics that include mercury corrosion, liquid-metal analytical chemistry, and liquid-metal properties. In the interest of comprehensive coverage, this meeting was restricted in scope. It was felt that topics not covered could be deferred to meetings under other auspices planned for the near future.