The Workshop on Parameterized and Exact Computation (IWPEC) is an - ternational workshop series
that covers research in all aspects of parameterized and exact algorithms and complexity and
especially encourages the study of parameterized and exact computations for real-world
applications and algori- mic engineering. The goal of the workshop is to present recent
research results including signi?cant work-in-progress and to identify and explore directions
for future research. IWPEC2009wasthefourthworkshopintheseries heldinCopenhagen D- mark during
September 10-11 2009. The workshop was part of ALGO 2009 which also hosted the 17th European
Symposium on Algorithms (ESA 2009) the 9th Workshop on Algorithmic Approaches for
Transportation Modelling Optimization and Systems (ATMOS 2009) and the 7th Workshop on Appr-
imation and Online Algorithms (WAOA 2009). Three previous meetings of the IWPEC series were
held in Bergen Norway 2004 Zu rich Switzerland 2006 and Victoria Canada 2008. At IWPEC
2009 we had two plenary speakers Noga Alon (Tel Aviv Univ- sity Israel) and Hans Bodlaender
(Utrecht University The Netherlands) giving 50-minutetalkseach.ProfessorAlonspokeon
ColorCoding BalancedHashing andApproximateCounting andProfessorBodlaenderon Kernelization:New
Upper and Lower Bound Techniques. Their respective abstracts accompanying the talks are
included in these proceedings. InresponsetotheCallforPapers
52papersweresubmitted.Eachsubmission was reviewed by at least three reviewers (most by at least
four). The reviewers were either Program Committee members or invited external reviewers. The
ProgramCommittee held electronic meetings using the EasyChair system went
throughthoroughdiscussions andselected25ofthesubmissionsforpresentation at the workshop and
inclusion in this LNCS volume.
