For proper planning and safe implementation of decommissioning of facilities, an accurate estimate of the radioactive inventory of the facility is needed (i.e. source term determination). The largest fraction of this inventory for nuclear power plants, research reactors and accelerator facilities is created by induced activation by neutrons or other particles (protons, electrons, ions). This publication provides information for facility operators and regulatory authorities involved in decommissioning planning and oversight of the process of assessment of the induced activation source term of a facility. It provides information on the selection and application of methodologies for the assessment of the induced activation source term for decommissioning purposes and provides an overview of approaches and practices currently available.