At the heart of the parapsychology (psi) battle are two types of phenomena: extra-sensory perception (ESP) and psycho-kinesis (PK). ESP is reception of information without any normal sensory means; PK is the use of the mind to influence physical states without any direct physical contact. Neither effect can be explained by ordinary science, so parapsychologists with experimental evidence that they are real are accused of bad science or bad faith or both. This collection of essays shows that a simple division into 'sceptics' and 'believers' cannot be made. The real struggle, for all researchers, is not with each other, but to get a secure hold on the subject itself.