  This work is devoted to the formulation and derivation of the
$\eta{-}\mu{/}$gamma and $\lambda{-}\mu{/}$gamma distributions which correspond
to physical fading models. These distributions are composite and are based on
the $\eta-\mu$ and $\lambda-\mu$ generalized multipath models, respectively,
and the gamma shadowing model. Novel analytic expressions are derived for the
corresponding envelope probability density functions. Importantly, the proposed
models provide accurate characterisation of the simultaneous occurrence of
multipath fading and shadowing effects which is achieved thanks to the
remarkable flexibility offered by their parameters that render them capable of
providing good fittings to experimental data associated with realistic
communication scenarios. This is additionally justified by the fact that they
include as special cases the widely known fading models such as Hoyt/gamma,
Nakagami-m/gamma and Rayleigh/gamma. As a result, they can be meaningfully
utilized in various analytical studies related to the performance evaluation of
digital communications over composite multipath/shadowing fading channels.
