This is a book about ion channels. It has been written mostly by physical scientists and mathematicians, even though the most widespread and important manifestation of ion channels is in biology, where they are essential to life in all its forms. How do non-biologists get involved in such investigations? Everyone will have their own particular story but, for ourselves, it was the heady combination of scientific curiosity, a wish to contribute to the fundamental understanding of natural phenomena that clearly have crucially important applications, and the realisation that some of our physics knowledge and expertise might be relevant.