This book constitutes the refereed proceedings of the 4th Fuji International Symposium on Functional and Logic Programming, FLOPS'99, held in Tsukuba, Japan, in November 1999.The 23 revised full papers presented were carefully reviewed and selected from a total of 51 submissions. The papers are devoted to various current aspects of functional and logic programming as well as to the integration of these two paradigms. Among the topics addressed are typing, partial evaluation, program transformations, parsing, formal verification, program analysis, static analysis, narrowing, etc.