  This thesis has been devoted to the study of different properties of hadrons
with one and two heavy quarks $c$ and/or $b$. All calculations have been done
in the framework of a nonrelativistic constituent quark model. In order to
check the sensitivity of our results to the inter--quark interaction we have
used five different quark--quark potentials. The spread in results gives an
estimation of theoretical uncertainties and so has been quoted.
  Most observables studied change only at the level of a few per cent when
changing the interaction potential.
  Another source of theoretical uncertainty is the use of nonrelativistic
kinematics in the evaluation of the orbital wave functions and the construction
of our nonrelativistic states, although we think that a good part of these
relativistic effects are contained in an effective way in the parameters of the
quark-quark potentials, which were adjusted in the original works to reproduce
the experimental spectra of mesons. Mesons wave functions have been evaluated
using a Numerov algorithm, while for baryons the three body problem has been
solved using a variational approach with ansatz wave functions that include
simplifications that arise from HQS and HQSS. To compute hadron decays we have
relied on the impulse approximation, which induces small axial and vector
current conservation violations due to binding effects. These binding effects,
though they affect some of the weak form factors analyzed, have little
influence on the decay widths.
