  The origin and the implications of higher dimensional effective operators in
4-dimensional theories are discussed in non-supersymmetric and supersymmetric
cases. Particular attention is paid to the role of general,
derivative-dependent field redefinitions which one can employ to obtain a
simpler form of the effective Lagrangian. An application is provided for the
Minimal Supersymmetric Standard Model extended with dimension-five R-parity
conserving operators, to identify the minimal irreducible set of such operators
after supersymmetry breaking. Among the physical consequences of this set of
operators are the presence of corrections to the MSSM Higgs sector and the
generation of "wrong"-Higgs Yukawa couplings and fermion-fermion-scalar-scalar
interactions. These couplings have implications for supersymmetry searches at
the LHC.
