  The existence of conservation laws is one of the most important requirement
of physical theories. Some of them, like energy conservation, knows no
experimental exception. However, the generalization of these conservation laws
to curved space presents many challenges. The implementation of conservation
laws in the General Relativity theory is revised, and the possibility of the
generalization of the usual expression is discussed. The Rastall's theory of
gravity, which considers a modification of the usual conservation of the
energy-momentum tensor, is discussed in more detail. Some applications of the
Rastall's theory to cosmology are presented, showing that it can lead to
competetive results with respect to the Standard Cosmological Model.
