Strong QED has attracted attention recently partly because many astrophysical phenomena have been observed to involve electromagnetic fields beyond the critical strength for electron-positron pair production and partly because terrestrial experiments will generate electromagnetic fields above or near the critical strength in the near future. In this talk we critically review QED phenomena involving strong external electromagnetic fields. Strong QED is characterized by vacuum polarization due to quantum fluctuations and pair production due to the vacuum instability. A canonical method is elaborated for pair production at zero or finite temperature by inhomogeneous electric fields. An algorithm is advanced to calculate pair production rate for electric fields acting for finite periods of time or localized in space or oscillating electric fields. Finally, strong QED is discussed in astrophysics, in particular, strange stars.
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