In December 2014, Hayabusa2 started its journey to 162173 Ryugu, a C-type asteroid likely to be primordial, thereby making this a voyage in both space and time. Hayabusa2 will begin its observations upon arrival at Ryugu in 2018. It will survey the asteroid's surface features, touch down on the asteroid, form an artificial crater by shooting an impactor, and collect sample materials both on and under the surface. In 2020, Hayabusa2 will return to Earth and release a re-entry capsule carrying material from Ryugu.This book contains papers describing the scientific objectives and instrumentation on Hayabusa2 and its landing package, MASCOT. The methods and developments presented in these papers have challenged the state-of-the-art of planetary exploration. This book is indispensable to understanding the results that Hayabusa2 will bring through its in situ and sample return exploration. Originally published in Space Science Reviews, Volume 208, Issue 1-4, July 2017