High-resolution X-ray spectroscopy has become a powerful tool for astrophysics since the launch of Chandra and XMM-Newton, ten years ago. The grating spectrometers on both instruments still continue to provide excellent data, while imaging calorimeters are being prepared for future missions like Astro-H and IXO. The synergy with other wavelength bands like the UV has been boosted by the addition of COS to HST. X-ray spectroscopy offers unique diagnostics to study almost any object in the Universe. This book contains review papers on highlights and the state-of-the-art of X-ray spectroscopy for a broad range of objects and on the prospects for future studies.