  The aim of the present paper is to establish a global theory of conformal
changes in Finsler geometry. Under this change, we obtain the relationships
between the most important geometric objects associated to $(M,L)$ and the
corresponding objects associated to $(M,\tilde{L})$,
$\widetilde{L}=e^{\sigma(x)} L$ being the Finsler conformal transformation. We
have found explicit global expressions relating the two associated Cartan
connections $\nabla$ and $\widetilde{\nabla}$, the two associated Berwald
connections $D$ and $\widetilde{D}$ and the two associated Barthel connections
$\Gamma$ and $\widetilde{\Gamma}$. The relationships between the corresponding
curvature tensors have been also found. The relations thus obtained lead in
turn to several interesting results.
  Among the results obtained, is a characterization of conformal changes, a
characterization of homotheties, some conformal invariants and conformal
$\sigma$-invariants. In addition, several useful identities have been found.
  Our global theory of conformal Finsler geometry is established within the
Pull-back approach, making simultaneous use of the Klein-Grifone approach. This
has been done via certain links we have found between both approaches (This
shows that these two approaches to global Finsler geometry are not alternatives
but rather complementary).
  Although our treatment is entirely global, the local expressions of the
obtained results, when calculated, coincide with the existing classical local
results.
