  The twistor diagram formalism for scattering amplitudes is introduced,
emphasising its finiteness and conformal symmetry. It is shown how MHV
amplitudes are simply represented by twistor diagrams. Then the
Britto-Cachazo-Feng recursion formula is translated into a simple rule for
composing twistor diagrams. It follows that all tree amplitudes in pure
gauge-theoretic scattering are expressed naturally as twistor diagrams. Further
implications are briefly discussed.
