Published online by Cambridge University Press: 12 April 2016
Important progress in our understanding of stellar chromospheres has occurred in the past few years as a result of new observations, developments in spectral line formation theory, and the application of that theory to the construction of detailed model chromospheres. Significant trends are beginning to emerge from such analyses, and we are on the threshold of a meaningful confrontation between purely theoretical models and the data. The range of stars thought to possess chromospheres may be widening, and we now have a better understanding of the enigmatic problem of why the Wilson-Bappu relation between Ca II emission core widths and stellar absolute visual magnitudes actually works.