It contains instructions for how to write 100 different alphabets. He also discusses the tools of the craft, including pens, brushes, and paper; and gives solid advice on paying attention to composition and layout.
Each alphabet contains an example of each letter, complete with stroke order, as well as instructions for pen angle and how to handle other, specific nuances. The book is organized chronologically and the author makes sure to point out the evolution of western scripts throughout time.
One thing to be aware of is that, in the more modern alphabets, he presents some scripts that are intended to be used with brushes or drafting pens, but the majority of the book is dedicated to those alphabets created with pen and nib.
I consider it an extremely valuable resource, and continue to refer to it time and time again as I try my hand at new scripts.
The other book I've started to use is The Bible of Illuminated Letters. This presents examples and patterns for the wonderful illuminated capital letters that one sees in illuminated manuscripts. The author, Margaret Morgan, begins by explaining the techniques used to create illuminated manuscripts, including a discussion of the specific tools and media used.
Then she breaks down the characteristics of lettering by time period and letter shape. She provides an in-depth example of one letter in each group, and then provides patterns for each of the others. She also points out which scripts are appropriate to use with the letters from each time period.
The result is a great reference for practicing the art of illuminated lettering. I can heartily recommend both books - they've provided valuable instruction and inspiration for me, and hopefully will for you, too.