The Editor of Artificial Life would like to express his gratitude to the people listed below, who anonymously reviewed papers for the journal during the preparation of Volume 21. Their generosity, judicious judgment, and prompt response substantially helped us publish a journal that both is timely and has exacting scientific standards. The responsibility for sustaining the quality and relevance of the Journal rests largely in the hands of our reviewers. We at the Journal, and all of our readers, are deeply indebted to them. It is a genuine pleasure to thank them collectively for their dedicated service. (If anyone has been inadvertently omitted from this list, we sincerely apologize and ask them to let us know so that we can include their name in a future list of referees.)

Andy Adamatsky

Martyn Amos

Tim Andersen

Claes Andersson

Takaya Arita

Ricardo Azevedo

Wolfgang Banzhaf

Peter Bentley

Michal Bidlo

Joachim Boldt

Josh Bongard

Alexandre Bouchard-Côté

Larry Bull

David Camacho

Alastair Channon

Jeff Clune

Miquel Cornudella

Jean-Paul Delahaye

Anna DePlazes

Ezequiel Di Paolo

Peter Dittrich

Marco Dorigo

Alan Dorin

Rene Doursat

Harold Fellerman

Jeff Fletcher

Ruedi Fuechslin

Carlos Gershenson

Kyrre Glette

Heather Goldsby

Angel Goni-Moreno

Laura Grabowski

Patrick Grim

Martin Hanczyc

Inman Harvey

Takashi Hashimoto

Helmut Hauser

Simon Hauser

Charlotte Hemelrijk

M. A. Hsieh

Phil Husbands

John Huss

Genki Ichinose

Jeff Jones

Olivier Martin

John McCaskill

Jon McCormack

Barry McMullin

Masoud Mirmomeni

Stefano Nichele

Stefano Nolfi

Charles Ofria

Nicholas Oliveto

Jean-Paul Peronard

Julien Pettre

Daniel Polani

Rashid Rashidzadeh

Steen Rasmussen

Jim Reggia

Craig Reynolds

John Rieffel

Sebastian Risi

Kepa Ruiz-Mirazo

David Sankoff

Hiroki Sayama

Paul Smaldino

Michael Spranger

Russell Standish

Pasquale Stano

Susan Stepney

Tadashi Sugawara

Uwe Tangen

Tim Taylor

Christof Teuscher

Federico Vaggi

Marco Villani

Nathaniel Virgo

Borys Wrobel

Andy Wuensche

Peter R. Wills