  Magnetic reconnection has been intensively studied in fully ionized plasmas.
However, plasmas are often partially ionized in astrophysical environments. The
interactions between the neutral particles and ionized plasmas might strongly
affect the reconnection mechanisms. We review magnetic reconnection in
partially ionized plasmas in different environments from theoretical,
numerical, observational and experimental points of view. We focus on
mechanisms which make magnetic reconnection fast enough to compare with
observations, especially on the reconnection events in the low solar
atmosphere. The heating mechanisms and the related observational evidence of
the reconnection process in the partially ionized low solar atmosphere are also
discussed. We describe magnetic reconnection in weakly ionized astrophysical
environments, including the interstellar medium and protostellar disks. We
present recent achievements about fast reconnection in laboratory experiments
for partially ionized plasmas.
