This review paper is devoted to presenting the standard multisymplectic
formulation for describing geometrically classical field theories, both the
regular and singular cases. First, the main features of the Lagrangian
formalism are revisited and, second, the Hamiltonian formalism is constructed
using Hamiltonian sections. In both cases, the variational principles leading
to the Euler-Lagrange and the Hamilton-De Donder-Weyl equations, respectively,
are stated, and these field equations are given in different but equivalent
geometrical ways in each formalism. Finally, both are unified in a new
formulation (which has been developed in the last years), following the
original ideas of Rusk and Skinner for mechanical systems.