  We present a new formalism for finding the low-energy effective Lagrangian of
Goldstinos and other fields. This Lagrangian is written using standard
superspace and the superfields are constrained to include only the light
degrees of freedom. The Goldstino resides in a (constrained) chiral superfield
X which is naturally identified at short distances. This allows us to exactly
compute the IR behavior of some correlation functions even in strongly coupled
theories with SUSY breaking. The Goldstino couplings above the scale of the
matter superpartners are determined by identifying X with the standard spurion.
At energies below the superpartners' scale, fermions, scalars (including
Goldstone bosons) and gauge fields are also described by constrained
superfields. Our framework makes it easy to find the leading order terms in the
Lagrangian and to control their corrections. It simplifies the derivation of
many known results and leads to new ones.
