  This is an informal paper that contains a list of ``things we know'' and
``things we do not know'' in manganites. It is adapted from the conclusions
chapter of a recent book by the author, {\it Nanoscale Phase Separation and
Colossal Magnetoresistance. The Physics of Manganites and Related Compounds},
Springer-Verlag, Berlin, November 2002. The main new result of recent manganite
investigations is the discovery of tendencies toward inhomogeneous states, both
in experiments and in simulations of models. The colossal magnetoresistance
effect appears to be closely linked to these mixed-phase tendencies, although
considerably more work is needed to fully confirm these ideas. The paper also
includes information on cuprates, diluted magnetic semiconductors, relaxor
ferroelectrics, cobaltites, and organic and heavy fermion superconductors.
These materials potentially share some common phenomenology with the
manganites, such as a temperature scale $T^*$ above the ordering temperature
where anomalous behavior starts. Many of these materials also present
low-temperature phase competition. The possibility of colossal-like effects in
compounds that do not involve ferromagnets is briefly discussed. Overall, it is
concluded that inhomogeneous ``clustered'' states should be considered a new
paradigm in condensed matter physics, since their presence appears to be far
more common than previously anticipated.
