Research on animal coloration is a vibrant area of biology currently involving evolutionary biologists, behavioural ecologists, psychologists, optical physicists, visual ecologists, geneticists and anthropologists. The proliferation of recent work requires that we take stock of the field, aiming to identify major themes, questions and future directions. This was the goal of the year-long Wissenschaftskolleg zu Berlin 'focus group ' (2015-2016), in which many of the authors in this issue participated either as fellows or visitors. The result is this 19-chapter theme issue, in which we pinpoint the breakthroughs and challenges in animal coloration research, focusing on production, perception, function and evolution. We also explore animal coloration research as it applies to humans. This theme issue is by no means exhaustive but our goal has been to summarize and synthesize the state of animal coloration research in 2017 and to chart courses for the future.The basic principles underlying animal coloration were formulated in a flurry of research during the second half of the 1800s and early part of the last century. These include the functional significance of coloration, involving protective coloration [1], disruptive coloration and countershading [2], sexually selected coloration [3], mimicry [4,5] and aposematism [6]. Use of colour phenotypes as genetic markers to study developmental processes and natural selection in the wild was critical to the early development of genetics and evolutionary theory [7]. In 1940, Cott's important volume [8] was a major milestone in our understanding of the functional significance of colour patterns, while Kettlewell [9] and Ford [10] spearheaded understanding of polymorphisms. In the 1960s and 1970s, we recognized that non-humans see the world differently from us, particularly in relation to ultraviolet perception [11]. Owing to the advent of spectrophotometry and digital imaging-combined with elegant laboratory and field studies, and large-scale comparative analyses-the field has since mushroomed. Now, the diversity and rapid pace of modern animal coloration research make it a particularly exciting interdisciplinary field.This issue provides an entry point to recent developments in the main areas of animal coloration research: colour production, perception, function and evolution, and application. We present the articles in this order. Each topic covered in this special issue touches on the interdisciplinary nature of animal coloration research [12]. We also emphasize that this field not only draws on many disciplines but also contributes fundamental knowledge to those disciplines, and generates solutions for societal problems too [13]. We hope that this theme issue will enable readers to make better sense of this broad, growing and dynamic area of biology.Competing interests. We declare we have no competing interests. Funding. We received no funding for this study.