This chapter presents the major principles of multistate demographic accounting developed by Philip Rees and extenddx by his team and others. It incorporates some aspects of multistate modelling in survival analysis.The account that results includes population flows, population stocks and durations of exposure and is a basis for the estimation of transition rates and probabilities for demographic modelling (life tables and projections). It is well-known that existing models of population projection, including those that have multiregional structures do not adequately handle the international migration
component of population dynamics. In many cases they are not adapted to the modelling of the populations of several countries as well as regions within those countries simultaneously. Thus, the incorporation of international migration into models of population dynamics is a key issue in terms of reducing forecasting error and one way to achieve this
is to use a matrix of flows between countries, rather than net migration, and to use emigration rates where possible.