This now out-of-print book by Alice Starmore is a great reference for Fair Isle knitting. Of course, there is the mandatory chapters on the history of Shetland knitting which I enjoyed reading. There are also chapters on FI patterns with charts and colour photos as well as a chapter with traditional garment recipes. All this is good but the part I am the most appreciative of is the detailed explanation of Shetland/FI technique which includes cut tubular knitting. Coupled with this is the chapter on designing your own garments using FI patterns and technique. The section on "planning a gansey" has been of great assistance to me on multiple occasions. This section gives instructions on sizing, gussets, necklines and sleeves.
My mate, Simon (MWK member in the UK) sent a copy of this book to me and I refer to it when I'm planning a new jumper. Now that I'm beginning to do stranded knitting, I'm appreciating it even more.
I know that this book is hard to find and then very dear once found (ebay prices hover around US$150.00! But, if you can get a copy, I highly recommend it.