  The BICEP experiment was designed specifically to search for the signature of
inflationary gravitational waves in the polarization of the cosmic microwave
background (CMB). Using a novel small-aperture refractor and 49 pairs of
polarization-sensitive bolometers, BICEP has completed 3 years of successful
observations at the South Pole beginning in 2006 February. To constrain the
amplitude of the inflationary B-mode polarization, which is expected to be at
least 7 orders of magnitude fainter than the 3 K CMB intensity, precise control
of systematic effects is essential. This paper describes the characterization
of potential systematic errors for the BICEP experiment, supplementing a
companion paper on the initial cosmological results. Using the analysis
pipelines for the experiment, we have simulated the impact of systematic errors
on the B-mode polarization measurement. Guided by these simulations, we have
established benchmarks for the characterization of critical instrumental
properties including bolometer relative gains, beam mismatch, polarization
orientation, telescope pointing, sidelobes, thermal stability, and timestream
noise model. A comparison of the benchmarks with the measured values shows that
we have characterized the instrument adequately to ensure that systematic
errors do not limit BICEP's 2-year results, and identifies which future
refinements are likely necessary to probe inflationary B-mode polarization down
to levels below a tensor-to-scalar ratio r = 0.1.

Cosmology and Nongalactic Astrophysics