  We present results for the nucleon electromagnetic form factors, including
the momentum transfer dependence and derived quantities (charge radii and
magnetic moment). The analysis is performed using O(a) improved Wilson fermions
in Nf=2 QCD measured on the CLS ensembles. Particular focus is placed on a
systematic evaluation of the influence of excited states in three-point
correlation functions, which lead to a biased evaluation, if not accounted for
correctly. We argue that the use of summed operator insertions and fit
ans\"atze including excited states allow us to suppress and control this
effect. We employ a novel method to perform joint chiral and continuum
extrapolations, by fitting the form factors directly to the expressions of
covariant baryonic chiral effective field theory. The final results for the
charge radii and magnetic moment from our lattice calculations include, for the
first time, a full error budget. We find that our estimates are compatible with
experimental results within their overall uncertainties.
