  We present the results of a realistic global fit of the Lagrangian parameters
of the Minimal Supersymmetric Standard Model assuming universality for the
first and second generation and real parameters. No assumptions on the SUSY
breaking mechanism are made. The fit is performed using the precision of future
mass measurements of superpartners at the LHC and mass and polarized
topological cross-section measurements at the ILC. Higher order radiative
corrections are accounted for whereever possible to date. Results are obtained
for a modified SPS1a MSSM benchmark scenario but they were checked not to
depend critically on this assumption. Exploiting a simulated annealing
algorithm, a stable result is obtained without any a priori assumptions on the
values of the fit parameters. Most of the Lagrangian parameters can be
extracted at the percent level or better if theoretical uncertainties are
neglected. Neither LHC nor ILC measurements alone will be sufficient to obtain
a stable result. The effects of theoretical uncertainties arising from unknown
higher-order corrections and parametric uncertainties are examined
qualitatively. They appear to be relevant and the result motivates further
precision calculations. The obtained parameters at the electroweak scale are
used for a fit of the parameters at high energy scales within the bottom-up
approach. In this way regularities at these scales are explored and the
underlying model can be determined with hardly any theoretical bias. Fits of
high-scale parameters to combined LHC+ILC measurements within the mSUGRA
framework reveal that even tiny distortions in the low-energy mass spectrum
already lead to inacceptable chi^2 values. This does not hold for ``LHC only''
inputs.
