Abstract
In the concluding chapter of this handbook, I consider some of the wider challenges that research into synaesthesia faces. I start with a brief overview of the first 200 years of synaesthesia research. I then go on to consider the issue of how synaesthesia might be defined and the kinds of phenomena that could fall under that umbrella term. In the second part of the chapter, I consider how science can study a subjective experience, the challenges in identifying the causes and consequences of synaesthesia, and finally some of the wider implications of synaesthesia for understanding the 'normal' mind and brain.