  A decade of X-ray stellar observations with Chandra and XMM-Newton has led to
significant advances in our understanding of the physical processes at work in
hot (magnetized) plasmas in stars and their immediate environment, providing
new perspectives and challenges, and in turn the need for improved models. The
wealth of high-quality stellar spectra has allowed us to investigate, in
detail, the characteristics of the X-ray emission across the HR diagram.
Progress has been made in addressing issues ranging from classical stellar
activity in stars with solar-like dynamos (such as flares, activity cycles,
spatial and thermal structuring of the X-ray emitting plasma, evolution of
X-ray activity with age), to X-ray generating processes (e.g. accretion, jets,
magnetically confined winds) that were poorly understood in the
pre-Chandra/XMM-Newton era. I discuss the progress made in the study of high
energy stellar physics and its impact in a wider astrophysical context,
focusing on the role of spectral diagnostics now accessible.
