  We propose a parametrization of anomalous Higgs-boson couplings that is both
systematic and practical. It is based on the electroweak chiral Lagrangian,
including a light Higgs boson, as the effective field theory (EFT) at the
electroweak scale $v$. This is the appropriate framework for the case of
sizeable deviations in the Higgs couplings of order $10\%$ from the Standard
Model, considered to be parametrically larger than new-physics effects in the
sector of electroweak gauge interactions. The role of power counting in
identifying the relevant parameters is emphasized. The three relevant scales,
$v$, the scale of new Higgs dynamics $f$, and the cut-off $\Lambda=4\pi f$,
admit expansions in $\xi=v^2/f^2$ and $f^2/\Lambda^2$. The former corresponds
to an organization of operators by their canonical dimension, the latter by
their loop order or chiral dimension. In full generality the EFT is thus
organized as a double expansion. However, as long as $\xi\gg 1/16\pi^2$ the EFT
systematics is closer to the chiral counting. The leading effects in the
consistent approximation provided by the EFT, relevant for the presently most
important processes of Higgs production and decay, are given by a few
(typically six) couplings. These parameters allow us to describe the properties
of the Higgs boson in a general and systematic way, and with a precision
adequate for the measurements to be performed at the LHC. The framework can be
systematically extended to include loop corrections and higher-order terms in
the EFT.
