In Canada, polar bear subpopulations are co-managed based on the best available scientific data and Indigenous Traditional Knowledge. One of the critical information needs for effective management is the number of polar bears that comprise a subpopulation, which is estimated by undertaking periodic population inventories. Population inventories are studies that not only provide an estimate of subpopulation size but also the uncertainty in the estimate. Inventories are often multi-year in duration, expensive, and logistically challenging given the remoteness and large geographical area to be covered. They are conducted on a cyclical basis, the frequency of which is largely determined by the scientific method used but also by management needs. Physical mark-recapture, genetic mark-recapture, and aerial survey are used in Canada to estimate subpopulation size.