This volume contains the papers presented at the 4th Fuji International S- posium on Functional and Logic Programming (FLOPS’99) held in Tsukuba, Japan, November 11–13, 1999, and hosted by the Electrotechnical Laboratory (ETL). FLOPS is a forum for presenting and discussing all issues concerning functional programming, logic programming, and their integration. The sym- sium takes place about every 1.5 years in Japan. Previous FLOPS meetings were held in Fuji Susuno (1995), Shonan Village (1996), and Kyoto (1998). 1 There were 51 submissions from Austria ( ),Belgium (2),Brazil(3),China 3 3 1 7 (1), Denmark (2), France (3 ), Germany (8), Ireland (1), Israel ( ), Italy (1 ), 4 3 12 1 Japan (9 ), Korea (1), Morocco (1), The Netherlands (1), New Zealand (1), 3 1 1 3 5 Portugal ( ), Singapore ( ), Slovakia (1), Spain (4 ), Sweden (1), UK (4 ), 2 3 4 6 1 and USA (2 ), of which the program committee selected 21 for presentation. In 4 addition, this volume contains full papers by the two invited speakers, Atsushi Ohori and Mario Rodríguez-Artalejo.