This handbook makes international guidance on estimating decommissioning costs more accessible by compiling material from two key reports: the International Structure for Decommissioning Costing (ISDC) of Nuclear Installations (NEA, 2012a) and Addressing Uncertainties in Cost Estimates for Decommissioning Nuclear Facilities (NEA, 2017). It includes, among other things, a common hierarchical reporting structure for decommissioning costing and ways to incorporate and present uncertainty and risk at any type of nuclear facility.