This book gives a comprehensive overview of our present understanding of the Earth's cryosphere, its changes and their consequences for mean sea level changes. Since the middle of the 19th century there has been an increase of sea level height by 20-25 cm. Some 8-10 cm of this is due to net losses from glaciers, the remainder being due to mass losses from land ice and thermal expansion of the oceans. The mean sea level rise is slowly accelerating; at present it is some 3 mm/year. Recent space observations made by the GRACE satellite combined with ocean temperature and volume measurements have enabled the separate contributions to sea level rise from melting ice and from thermal expansion to be better estimated. The estimation of mean sea level change is complicated by changes in land level due to tectonic effects and to ongoing changes following the latest major glaciation. The book gives an up-to-date survey of our present knowledge of this crucial subject.