  We present a consistent renormalization scheme for the CP-conserving
Two-Higgs-Doublet Model based on $\overline{MS}$ renormalization of the mixing
angles and the soft-$Z_2$-symmetry-breaking scale $M_{sb}$ in the Higgs sector.
This scheme requires to treat tadpoles fully consistently in all steps of the
calculation in order to provide gauge-independent $S$-matrix elements. We show
how bare physical parameters have to be defined and verify the gauge
independence of physical quantities by explicit calculations in a general
$R_{\xi}$-gauge. The procedure is straightforward and applicable to other
models with extended Higgs sectors. In contrast to the proposed scheme, the
$\overline{MS}$ renormalization of the mixing angles combined with popular
on-shell renormalization schemes gives rise to gauge-dependent results already
at the one-loop level. We present explicit results for electroweak NLO
corrections to selected processes in the appropriately renormalized
Two-Higgs-Doublet Model and in particular discuss their scale dependence.
