This chapter discusses two phenomena that involve low-energy particles, most importantly neutrons: the transmission of photons and neutrons through penetrations and the control of neutron “skyshine.” All neutron-producing accelerators need to control the transmission of neutrons, and also photons, through penetrations since all have accessways to permit entry of personnel and equipment. The first widely documented calculation of the skyshine radiation field was that of Lindenbaum. A more rigorous treatment has been reported by G. R. Stevenson and R. H. Thomas based on the work of Alsmiller et al. and Nakamura and Kosako. The prescription of Stevenson and Thomas is used to calculate the dose equivalent in one hour at 200 m. The albedo of neutrons is less energy dependent and angle dependent than that of photons scattered under comparable scenarios. For neutrons, the more complex physics of their transport discourages the use of a formula similar to that employed previously using photon albedo coefficients.