  We present an analytical calculation of the extreme value statistics for dark
matter halos - that is, the probability distribution of the most massive halo
within some region of the universe of specified shape and size. Our calculation
makes use of the counts-in-cells formalism for the correlation functions, and
the halo bias derived from the Sheth-Tormen mass function.
  We demonstrate the power of the method on spherical regions, comparing the
results to measurements in a large cosmological dark matter simulation and
achieving good agreement. Particularly good fits are obtained for the most
likely value of the maximum mass and for the high-mass tail of the
distribution, relevant in constraining cosmologies by observations of most
massive clusters.
