This book, in two parts, Why and How, is a result of fifty years of a variety of educational efforts. This book explains, in studied detail, why solo Sudoku is a potentially powerful training tool to impact the cognitive skills of most of humanity. Training pure logical thinking capabilities, known as fluid intelligence, can give children mental advantages that produce better decision making and problem solving that come from optimal management of information. Repeating logical problem solving about 50 times each puzzle trains logical thinking. Sudoku makes clear the need for relevant information, accuracy, sufficient information and a variety of patterns, all of which lead to our best results when encountering all mental challenges. Sudoku appeals to anyone who can count to nine. Sudoku is immune to any differences of religion, language, politics, nationality, race. ethnicity, age or gender. Sudoku is very practical, being cheap, requiring no technology, and can be done anywhere any time, requiring only a pencil and a flat place to write. When done in teams, Sudoku is beneficial in developing social skills such as communication, collaboration, cooperation and leadership. Written primarily for educators, this book is also applicable in prisons, hospitals and senior living communities, where self-esteem, independent thinking and boredom can be influenced.