This book presents the proceedings of the 6th International Conference on Attosecond Physics (ATTO), one of the most important conferences series in the field of attoscience. ATTO 2017 was held in Xi’an, China, from July 2 to 7, 2017. These proceedings cover all the aspects of attosecond physics from sources and metrology to applications. Topics included are attosecond pulse generation and characterization; high-order harmonic generation and applications; ultrafast phenomena on attosecond and femtosecond timescales; next generation drivers for attosecond pulse and high-order harmonic generation; new sources and applications of coherent ultrafast XUV and X-rays, as well as time-resolved photon, electron, and ion spectroscopy.