  We review on-shell and unitarity methods and discuss their application to
precision predictions for LHC physics. Being universal and numerically robust,
these methods are straight-forward to automate for next-to-leading-order
computations within Standard Model and beyond. Several state-of-the-art results
including studies of W/Z+3-jet and W+4-jet production have explicitly
demonstrated the effectiveness of the unitarity method for describing
multi-parton scattering. Here we review central ideas needed to obtain
efficient numerical implementations. This includes on-shell loop-level
recursions, the unitarity method, color management and further refined tricks.
