  We construct the general two-Higgs doublet model effective field theory where
the effects of additional new physics are parameterized by operators up to mass
dimension-six. We further transform this effective theory to the Higgs basis
and provide matching of the Wilson coefficients between the two descriptions.
We illustrate the advantages of the Higgs basis which include the separation of
operators that modify standard model couplings and masses from operators that
contribute to scattering processes only, transparent correlations between
scattering processes resulting from the same operator, and derivation of
correlations between different operators in specific UV completions. For
completeness, we also construct specific versions corresponding to four types
of two-Higgs doublet models: type-I, -II, -X, and -Y, distinguished by $Z_2$
symmetries which restrict the couplings of the Higgs doublets to standard model
fermions. Furthermore, we derive general vacuum and stability conditions of the
scalar potential in the presence of higher-dimensional terms.
