"This book covers the dynamics of young stellar systems. ? this is both a good introduction to the field, and a useful reference for those who already work in the area. ? This is a great book for both observers and theorists in any area around star formation, star clusters/associations, and galactic dynamics - especially timely with Gaia data arriving soon. I gave it to my PhD students with the instruction 'read this from cover to cover - it's really useful'." (Simon Goodwin, The Observatory, Vol. 136 (1255), December, 2016)