FOOL became FOOL/WOOD in 2006, joining forces with the Workshop on Object-Oriented Developments. Although last year the name returned to FOOL, it is the fourth workshop in that successful merger. FOOL'09 will be held in Savannah, Georgia, on Saturday, 24 January 2009, the day after POPL'09. Specific topics addressed in past workshops have included semantics, object calculi, type theory, and program verification of object-oriented languages. More recently special efforts have been made to include contributions on foundational issues related to concurrent and distributed object-oriented languages, and database languages with object-oriented features.