  We review some aspects related to orbital degrees of freedom in manganites.
The Mn$^{3+}$ ions in these compounds have double orbital degeneracy and are
strong Jahn-Teller ions, causing structural distortions and orbital ordering.
We discuss ordering mechanisms and the consequences of orbital order. The
additional degeneracy of low-energy states and the extreme sensitivity of the
chemical bonds to the spatial orientation of the orbitals result in a variety
of competing interactions. This quite often leads to frustration of classical
ordered states and to the enhancement of quantum effects. Quantum fluctuations
and related theoretical models are briefly discussed, including the occurence
of resonating orbital bonds in the metallic phase of the colossal
magnetoresistance manganites.
