This book is a community effort! We are a community of researchers who are fascinated by the behaviour of animals. We endeavour to describe behaviour and understand the proximate and ultimate mechanisms of behaviour. In this pursuit we are only few among the many other researchers in animal behaviour and behavioural ecology. What sets us apart is our choice of model: spiders. If you, valued reader, assume we have chosen to work on spiders because we have been ensnared by their curious biology you may be partly right. The main reason, however, why we address theoretical questions about behaviour in spiders is because we recognise their scientific value, versatility and often superiority over other animal models. We believe that the utility of spiders in behavioural research is grossly underestimated. The motivation behind this book is to showcase spider behaviour to the broader research community. The ten chapters of the book describe most aspects of spider behaviour, from foraging to communication to mating and deception. Some behaviour crosses these, often arbitrary, classifications, and hence it is not surprising to find a discussion of the same species and behaviour in more than one chapter. Some chapters are more extensive than others, not because that particular topic is more important than other topics, but primarily because we decided not to subdivide certain chapters into two or more smaller chapters.