Book by Chris Fellows - a dissection of skiing fitness and technique.
This book is very detailed and a great read for the coach and the involved parent or skier. I find myself wishing though that there would be more actionable items in here, more specificity, like say the Essentials of Skiing++. Sure, it is full of drills and exercises and other things that a skier can do to improve, but it seems to me that it could have more guidance, more direction.
The book starts with an overview of the components of skiing, including fitness and technique and an extensive assessment sheet, that will identify your "profile" and put you in one of 4 categories:
Then, the book starts with drills and exercises, most of which are very good and then goes through development programs for each of the types of skiers.
It is definitely worth re-reading every now and then, especially when creating detailed training and development plans - not for the average skier, perhaps.