The Trajectoire (Career path) model, created by DREES, is a dynamic microsimulation model with the main objective of producing projections of future retired populations and their pension levels. This model makes it possible to consider different economic scenarios. It is also capable of simulating changes to the pension system and evaluating the long-term impacts. This analysis can be conducted at the individual level (change in the age of taking retirement, pension variations, pension duration) or aggregated levels (the number of retired persons and persons entering retirement, the mas of pensions). This model is based on the Inter-Regime Sample of Contributors (Échantillon Interrégimes de Cotisants: EIC) which charts, up to 2009, the career paths of a representative sample of 350,000 individuals. Drawn from administrative data from pension funds, this sample brings together a wealth of precise information on career factors, and can provide the basis for a detailed simulation of the acquisition of direct rights for almost all French pension funds and, for this reason in particular, can provide a perspective that is complementary to other existing microsimulation models. The model begins by extending the careers of individuals included in the EIC by means of a module for the transition between statuses in the labour market. The wages are then simulated based on a panel data model. The model then simulates pension rights by drawing on two pre-existing tools: the Promess module for simulating the age at which retirement will be taken, and the Calipher programme, which calculates direct-entitlement pension. The study of the pension reform of 20 January 2014 serves to illustrate the way in which Trajectoire estimates the impact of a legislative change and is able to define the individual and global effects of a reform.