The goal of the Commercial Users of Functional Programming series of workshops is "to build a community for users of functional programming languages and technology". The fourth workshop in the series took place in Freiburg, Germany on 4th October 2007, co-located with the International Conference on Functional Programming. The workshop is growing rapidly, having started in Snowbird in 2004 with 25 participants, increasing to 40 in Tallinn in 2005 and 57 in Portland in 2006, and finally to 104 registered in 2007. We take this growth as evidence of a sea change in attitudes to functional programming: from being an academic pursuit, functional programming is rapidly becoming a sought-after technology with increasingly broad applications.

For the first time this year, we received more offers of presentations than would fit in the available time. The eventual schedule included an invited talk by Xavier Leroy, eleven contributed presentations, and an energetic concluding discussion led by Don Syme. Many of the slides for these presentations are available from the CUFP home page (http://cufp.functionalprogramming.com).