This text is aimed at presenting the basic ingredients necessary
to understand shell-type supernova remnants, with particular
emphasis on their X-ray emission.
The other observational domains (radio and optical) are mentioned
but not discussed in depth.
I do not discuss at all the synchrotron nebulae, such as the Crab Nebula,
which are also relics of a supernova explosion, but are driven by
the remaining pulsar rather than the mechanical energy of the supernova.
After a brief historical introduction, I describe the hydrodynamic
concepts used for supernova remnants. Then I describe the Sedov model
governing middle-aged supernova remnants, and the coronal conditions
under which the X-ray emission is computed.
Quantitative formulae are given for the Sedov model,
allowing to relate X-ray observations to energy, ambient density and age.
A chapter describes the initial (young) and final (old) stages
of supernova remnants.
Cosmic-ray acceleration at shocks is described, as well as its
consequences on supernova remnants. The final chapter deals
with statistical issues.