  We present an on-shell formalism for superamplitudes of pure N<4 super
Yang-Mills theory. Two superfields, Phi and Phi^+, are required to describe the
two CPT conjugate supermultiplets. Simple truncation prescriptions allow us to
derive explicit tree-level MHV and NMHV superamplitudes with N-fold SUSY. Any
N=0,1,2 tree superamplitudes have large-z falloffs under super-BCFW shifts,
except under [Phi,Phi^+>-shifts. We show that this `bad' shift is responsible
for the bubble contributions to 1-loop amplitudes in N=0,1,2 SYM. We evaluate
the MHV bubble coefficients in a manifestly supersymmetric form and demonstrate
for the case of four external particles that the sum of bubble coefficients is
equal to minus the tree superamplitude times the 1-loop beta-function
coefficient. The connection to the beta-function is expected since only bubble
integrals capture UV divergences; we discuss briefly how the minus sign arises
from UV and IR divergences in dimensional regularization. Other applications of
the on-shell formalism include a solution to the N^{K}MHV N=1 SUSY Ward
identities and a clear description of the connection between 6d superamplitudes
and the 4d ones for both N=4 and N=2 SYM. We outline extensions to N<8
supergravity.
