I have not conducted very precise benchmarks. There is however one main reason for Scala programs to be faster than the programs you will be able to write with the elements developed in the book: optimization. Most Scala structures are implemented in imperative style when maximum performance is needed, using mutable variables internally. On contrary, most structures presented in the book are implemented in functional style, for pedagogical reasons. If we were designing a functional library, we would probably be tempted to do the same as Scala. However, most of the functional structures that I present have been used in production for several years (starting with a Java 6 version!) giving good enough performance.