  We calculate, for the first time using unquenched lattice QCD, form factors
for the rare decay B -> Kll in and beyond the Standard Model. Our lattice QCD
calculation utilizes a nonrelativistic QCD formulation for the b valence
quarks, the highly improved staggered quark formulation for the light valence
quarks, and employs the MILC 2+1 asqtad ensembles. The form factor results,
based on the z expansion, are valid over the full kinematic range of q^2. We
construct the ratios f0/f+ and fT/f+, which are useful in constraining new
physics and verifying effective theory form factor symmetry relations. We also
discuss the calculation of Standard Model observables.
