  A geometric formulation of Higgs Effective Field Theory (HEFT) is presented.
Experimental observables are given in terms of geometric invariants of the
scalar sigma model sector such as the curvature of the scalar field manifold
$\mathcal M$. We show how the curvature can be measured experimentally via
Higgs cross-sections, $W_L$ scattering, and the $S$ parameter. The one-loop
action of HEFT is given in terms of geometric invariants of $\mathcal M$. The
distinction between the Standard Model (SM) and HEFT is whether $\mathcal M$ is
flat or curved, not whether the scalars transform linearly or non-linearly
under the electroweak group.
