Nobel laureate Niko Tinbergen laid the foundations for the scientific study of animal behaviour with his work on causation, development, function and evolution. In this book, an international cast of leading animal biologists reflect on the enduring significance of Tinbergen's groundbreaking proposals for modern behavioural biology. It includes a reprint of Tinbergen's original article on the famous 'four whys' and a contemporary introduction, after which each of the four questions are discussed in the light of contemporary evidence. There is also a discussion of the wider significance of recent trends in evolutionary psychology and neuroecology to integrate the 'four whys'. With a foreword by one of Tinbergen's most prominent pupils, Aubrey Manning, this wide-ranging book demonstrates that Tinbergen's views on animal behaviour are crucial for modern behavioural biology. It will appeal to graduate students and researchers in animal behaviour, behavioural ecology and evolutionary biology.