This is an extremly important book by the great and most influencial music theorist of the 20th Century, Henrich Schenker. In this book, he speaks about contemporary performance practice and focuses in particularly on the technique of piano playing and piano practicing. There are chapters dedicated to specific techniques such as legato-playing and pedalling, and detailed discussions on dynamics, fingering, and rests. I highly recommend this book to all the musicians out there, it is simply too important to be overlooked.