  In a superconductor electrons form pairs and electric transport becomes
dissipation-less at low temperatures. Recently discovered iron based
superconductors have the highest superconducting transition temperature next to
copper oxides. In this article, we review material aspects and physical
properties of iron based superconductors. We discuss the dependence of
transition temperature on the crystal structure, the interplay between
antiferromagnetism and superconductivity by examining neutron scattering
experiments, and the electronic properties of these compounds obtained by angle
resolved photoemission spectroscopy in link with some results from scanning
tunneling microscopy/spectroscopy measurements. Possible microscopic model for
this class of compounds is discussed from a strong coupling point of view.
