["Population and Development Review, Volume 47, Issue 3, Page 639-663, September 2021. ", "\nAbstract\nAcross the world, populations have transitioned to inhabiting urban spaces, and in low‐ and middle‐income countries the proportion of people living in cities is expected to continue to increase. Anticipation of this fundamental process calls for a better understanding of the demographic factors that drive the urban transition. By indirectly estimating the joint contribution of migration and administrative reclassification to urban transition in 129 countries using urban and rural population by age and sex data available from the United Nations over 1985–2015, we find that differences in natural increase between the rural and urban sectors explain most of the urbanization over the 30‐year period examined. Over the urban transition, the role of migration and reclassification declines and becomes negligible. Despite data limitations, we confirm that it is misleading to view migration as fueling urbanization in low‐ and middle‐income countries.\n"]