  Starting from the three-dimensional Cosserat elasticity, we derive a
two-dimensional model for isotropic elastic shells. For the dimensional
reduction, we employ a derivation method similar to that used in classical
shell theory, as presented systematically by Steigmann in [J. Elast.
\textbf{111}: 91-107, 2013]. As a result, we obtain a geometrically nonlinear
Cosserat shell model with a specific form of the strain-energy density, which
has a simple expression with coefficients depending on the initial curvature
tensor and on three-dimensional material constants. The explicit forms of the
stress-strain relations and the local equilibrium equations are also recorded.
Finally, we compare our results with other 6-parameter shell models and discuss
the relation to the classical Koiter shell model.
