  A measurement of the total $pp$ cross section at the LHC at $\sqrt{s}=7$ TeV
is presented. In a special run with high-$\beta^{\star}$ beam optics, an
integrated luminosity of 80 $\mu$b$^{-1}$ was accumulated in order to measure
the differential elastic cross section as a function of the Mandelstam momentum
transfer variable $t$. The measurement is performed with the ALFA sub-detector
of ATLAS. Using a fit to the differential elastic cross section in the $|t|$
range from 0.01 GeV$^2$ to 0.1 GeV$^2$ to extrapolate to $|t|\rightarrow 0$,
the total cross section, $\sigma_{\mathrm{tot}}(pp\rightarrow X)$, is measured
via the optical theorem to be: $$\sigma_{\mathrm{tot}}(pp\rightarrow X) = 95.35
\; \pm 0.38 \; ({\mbox{stat.}}) \pm 1.25 \; ({\mbox{exp.}}) \pm 0.37 \;
(\mbox{extr.}) \; \mbox{mb},$$ where the first error is statistical, the second
accounts for all experimental systematic uncertainties and the last is related
to uncertainties in the extrapolation to $|t|\rightarrow 0$. In addition, the
slope of the elastic cross section at small $|t|$ is determined to be $B =
19.73 \pm 0.14 \; ({\mbox{stat.}}) \pm 0.26 \; ({\mbox{syst.}}) \;
\mbox{GeV}^{-2}$.
