NeutronsNeutron crystallography have a unique role to play in determining the structure and dynamics of biological macromolecules and their complexes. The similar neutron scattering magnitude from deuterium (2H), carbon (C), nitrogen (N), and oxygen (O) nuclei, means that the effect of atomic vibration in lowering the visibility of these atoms in Fourier maps is no worse for the deuterium atoms, unlike the X-ray case. Moreover, the negative scattering length of the common protium isotope (1H) and the positive scattering length of deuterium allows the well-known neutron 1H/2H contrast variation method to be applied. Furthermore, as there is no problem with radiation damage using neutrons as the diffraction probe, unlike X-rays, room temperature neutron data collection studies are completely viable. Unfortunately, even with these advantages, the low flux of existing neutron facilities means that neutron biological crystallography is not going to be a high throughput technique due to the long measuring runs at present e.g. typically between one to two weeks or more.