The report provides an up-to-date overview of major population trends in the least developed countries (LDCs), landlocked developing countries (LLDCs) and small island developing States (SIDS) in connection with the critical development challenges they face. The groups of countries in special situations comprise 110 countries (45 LDCs, 32 LLDCs, and 57 SIDS) located in all regions of the world. The report focuses on differences and similarities in demographic characteristics between regional subgroups of the three categories of countries. It highlights levels and trends in population size, structure and distribution, mortality, fertility and international migration from 2000 to 2050, while also discussing the implications of these demographic trends for achieving the relevant SDGs.