With the imminent launch of XRISM, the field of X-ray astronomy is about to enter a new
era of spatially-resolved, high-resolution spectroscopy, as driven by the technologies
of a novel X-ray imaging spectrometer based on an array of microcalorimeters. As shown
by sounding-rocket experiments and the Hitomi satellite in the past, the prospect of
such a spectrometer in bringing major scientific breakthroughs is highly exciting. All
eyes will be on XRISM to witness the full potential of microcalorimeters with a
dedicated X-ray mission. Looking further into the future, ESA has approved the Athena
satellite for launch in the early 2030s in Europe, while key technology development is
ongoing for a number of other X-ray mission proposed in China, Japan, and US. These
missions will employ a new generation of microcalorimeters, based on superconducting
technologies, which is expected to deliver even more superior spectral resolution. In
this talk, I will briefly review key milestones in the development of X-ray astronomy,
leading to the new era of the field, and highlight some of the key unresolved scientific
issues that are expected to be addressed in the new era.