  Altermagnetism is a recently identified magnetic symmetry class combining
characteristics of conventional collinear ferromagnets and antiferromagnets,
that were regarded as mutually exclusive, and enabling phenomena and
functionalities unparalleled in either of the two traditional elementary
magnetic classes. In this work we use symmetry and ab initio theory to explore
X-ray magnetic circular dichroism (XMCD) in the altermagnetic class. Our
results highlight the distinct phenomenology in altermagnets of this
time-reversal symmetry breaking response, and its potential utility for
element-specific spectroscopy and microscopy in altermagnets. As a
representative material for our XMCD study we choose $\alpha$-MnTe with the
compensated antiparallel magnetic order in which an anomalous Hall effect has
been already demonstrated both in theory and experiment. The predicted
magnitude of XMCD lies well within the resolution of existing experimental
techniques.
