  A novel approach to study electroweak physics at one-loop level in generic
${\rm SU(2)_L \times U(1)_Y}$ theories is introduced. It separates the 1-loop
corrections into two pieces: process specific ones from vertex and box
contributions, and universal ones from contributions to the gauge boson
propagators. The latter are parametrized in terms of four effective form
factors $\bar{e}^2(q^2)$, $\bar{s}^2(q^2)$, $\bar{g}_Z^2(q^2)$ and $\bar{g}_W^2
(q^2)$ corresponding to the $\gamma\gamma$, $\gamma Z$, $ZZ$ and $WW$
propagators. Under the assumption that only the Standard Model contributes to
the process specific corrections, the magnitudes of the four form factors are
determined at $q^2=0$ and at $q^2=\mmz$ by fitting to all available precision
experiments. These values are then compared systematically with predictions of
${\rm SU(2)_L \times U(1)_Y}$ theories. In all fits $\alpha_s(\mz)$ and
$\bar{\alpha}(\mmz)$ are treated as external parameters in order to keep the
interpretation as flexible as possible. The treatment of the electroweak data
is presented in detail together with the relevant theoretical formulae used to
interpret the data. No deviation from the Standard Model has been identified.
Ranges of the top quark and Higgs boson masses are derived as functions of
$\alpha_s(\mz)$ and $\bar{\alpha}(\mmz)$. Also discussed are consequences of
the recent precision measurement of the left-right asymmetry at SLC as well as
the impact of a top quark mass and an improved $W$ mass measurement.
