The Mitten Handbook by Mary Scott Huff

The Mitten Handbook is more than an instruction book. It provides a list of mitten ingredients (thumbs, cuffs, and top-down or bottom-up construction) then outlines the best tools and techniques for knitters to create their own unique mittens. The book is organized into three sections: the first shows mitten elements, with choices that make getting custom results easy.
the second section provides 20 complete mitten patterns, and the third section covers the key aspects of construction, including how to measure for the perfect fit, yarn and gauge considerations, and which direction to knit.