The discovery that a significant part of the energy emission from the solar corona is concentrated along well-defined curved paths – called loops – represents a major advance in our understanding of the Sun. Such plasma loops are the basic structural elements of the corona, particularly in and over active regions. Moreover, they play a decisive role in the origin and physics of solar flares. Our new insight is due largely to the wealth of space observations of the Sun obtained, in particular, from the manned satellite Skylab (1973–4) and the unmanned satellites Solar Maximum Mission and Hinotori which followed. Ground-based observations in the visible and microwave regions of the electromagnetic spectrum have also played a vital role. The literature on coronal plasma loops is vast and includes not only hundreds of research papers but also the proceedings of numerous symposia and workshops. This book presents for the first time a comprehensive, unified and well-illustrated account of the properties of coronal loops based on the best space and ground-based observations currently available (Chapters 2–4). A magnetohydrodynamic analysis of the stability and dynamics of loops is presented in Chapter 5, while the final chapter (Chapter 6) explores the wider implications of the loop regime on our understanding of both the solar corona and stellar coronae.