Sister Mary Mercedes, O.P. (1871-1965), a Dominican Sister, was a teacher for more than fifty years. She wrote the original Book of Courtesy in 1910 for use at the Dominican Convent Upper School in San Rafael, and later at the San Domenico School in San Anselmo. To honor their fiftieth reunion and the sesquicentennial of the Dominican Sisters in California, the Class of 1950 -- most of them grandmothers, all of them experienced in the joys and sorrows of life and profoundly influenced by this book -- revised Sister Mercedes' original volume in the hope of passing on its wisdom to their grandchildren, who inherit a world sorely in need of her message.