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Published online by Cambridge University Press: 26 May 2016
SiO, H2O and OH masers are ubiquitous in the circumstellar envelopes (CSEs) of oxygen-rich, red giant stars. Radio interferometry allows the imaging of stellar maser emission down to sub-milliarcsecond scales. Such observations reveal asymmetry, inhomogeneity and apparent clumpiness in the extended atmosphere and surrounding envelope of the star. The studies place constraints on processes which are seldom included in models. Here, I review the observational data on stellar masers and discuss their implications for our understanding of the mass-loss and evolution of red giant stars.