The Eleventh ACM SIGPLAN International Conference on Functional Programming (ICFP 2006) took place on September 18–20, 2006 in Portland, Oregon. ICFP 2006 provides a forum for researchers and developers to hear about the latest work on the design, implementation, principles, and uses of functional programming. The conference covers the entire spectrum of work, from theory to practice, and beyond. There were 74 submissions, of which the program committee selected 24 for presentation at the conference. Following the conference, the program committee selected eight papers for which the authors were invited to submit extended versions for this special issue of JFP. The seven papers that appear in this volume were reviewed, revised, and accepted following standard JFP procedures. These papers cover a wide range of topics related to functional programming, including programming, program verification, language design, language development, program transformation, and program analysis. This range of topics reflects the variety of the work presented at the ICFP conference.