Supernova remnants (SNRs) hold an important place in the history of X-ray astronomy, being associated with many observational "firsts." The first radio/optical object associated with an X-ray source was the Crab Nebula. Cassiopeia A (Cas A) was the first X-ray source for which an X-ray spectrum showed evidence for line emission. SNRs were among the first extended X-ray sources to be imaged, and with their complex, filamentary structure, they are also among the most photogenic X-ray sources.

This review attempts to capture the most important insights gained into the physics of SNRs during the past few years of X-ray observations. Before doing so, the stage will be set by briefly describing SNR evolution, the significance of X-ray emission, and some of the key results from earlier X-ray observations. Interestingly, many of the fundamentally important recent results were hinted at by early observations (such as ionization nonequilibrium and nonthermal emission from shock accelerated electrons); bringing them to light required the enhanced capabilities of the most recent generation of observatories. This review focuses on the extended remnants, and includes little about either their compact central objects or pulsar wind nebulae. These objects merit an entire review in and of themselves.

This review also addresses X-ray observations of supernovae (SNe). This is relatively new area of X-ray studies, and for the most part, the X-ray emission mechanism of the SNe detected thus far is largely the same as that at work in their older cousins.

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