  Relativistic Hamiltonians are defined as the sum of relativistic one-body
kinetic energies, two- and many-body interactions and their boost corrections.
We review the calculation of the boost correction of the two-body interaction
from commutation relations of the Poincare group and show that its important
terms can be easily understood from classical relativistic mechanics. The boost
corrections for scalar- and vector- meson-exchange interactions, obtained from
relativistic field theory, are shown to be in agreement with the results of the
classical calculation. These boost corrections are also shown to be necessary
to reproduce the known results of relativistic mean-field theories. We conclude
with comments on the relativistic boost operator for the wave function of a
nucleus. Several of the results presented in this pedagogical article are
known. We hope that a better understanding of relativistic Hamiltonians and
their relation to relativistic field theory is obtained by putting them
together with a few new relations.
