  Solar flares are often accompanied by filament/prominence eruptions,
sometimes leading to coronal mass ejections (CMEs). By analogy, we expect that
stellar flares are also associated with stellar CMEs whose properties are
essential to know the impact on exoplanet habitability. Probable detections of
stellar CMEs are still rare, but in this decade, there are several reports that
(super-)flares on M/K-dwarfs and evolved stars sometimes show blue-shifted
optical/UV/X-ray emissions lines, XUV/FUV dimming, and radio bursts. Some of
them are interpreted as indirect evidence of stellar prominence eruptions/CMEs
on cool stars. More recently, evidence of stellar filament eruption, probably
leading to a CME, is reported even on a young solar-type star (G-dwarf) as a
blue-shifted absorption of H$\alpha$ line associated with a superflare.
Notably, the erupted masses for superflares are larger than those of the
largest solar CMEs, indicating severe influence on exoplanet environments. The
ratio of the kinetic energy of stellar CMEs to flare energy is significantly
smaller than expected from the solar scaling relation and this discrepancy is
still in debate. We will review the recent updates of stellar CME studies and
discuss the future direction in this paper.
