Many populations of migratory bird species are rapidly declining. As a requisite for targeting effective conservation efforts it is essential to determine the whereabouts of migrants year-round. However, our knowledge of migratory routes and spatial-temporal occurrence across periods of the annual cycle is still limited for most species. We used light-level geolocators to describe in detail the migration system of Barn Swallows Hirundo rustica breeding in southwestern Spain and wintering across West Africa. We were able to successfully retrieve year-round data for 38 individuals and reconstructed their migratory routes using FLightRR package. Many of the studied individuals remained for some time in summer wandering through southern Spain and northern Morocco, a period that we defined as pre-migration. The studied swallows started their autumn migration on average on August 18^th, stopping over to refuel in northwestern Morocco and southern Mali. On average the tagged individuals arrived on September 3^rd at their wintering areas, which were located across Ivory Coast and surrounding countries, in localities dominated by savannahs, grasslands and crops. After wintering, swallows started the spring migration January 26^th on average, stopping over in Senegal and Mauritania. They arrived back at the Spanish breeding colonies February 18^th on average (from mid-January to mid-March). Surprisingly, during the autumn migration, one of the tagged individuals travelled to England before returning south and spending a short wintering period in northwestern Spain.—López-Calderón, C., Magallanes, S., Marzal, A. & Balbontín, J. (2021). The migration system of Barn Swallows Hirundo rustica breeding in southwestern Spain and wintering across west Africa. Ardeola, 68: 335-354.