If you are interested in writing Flash Fiction, or you are already an established Flash Fiction writer, then I highly recommend this brilliant guide to the genre. Cleverly, each section is written as a slice of Flash and perfectly demonstrates the form. This book is packed with wisdom on the process, art and ethos behind Flash Fiction. I read it quickly and am re-reading to highlight the sections I find useful, and literally even page is marked up (I discarded the sticky notes early on because I was going to run out!).
For me this is up there with Stephen King's 'On Writing' for insights and quotes on what writing is all about, one I will continue to revisit again and again.