We studied local adaptation to contrasting environments using an emerging model organism of evolutionary plant biology – the outcrossing, perennial herb Arabidopsis lyrata ssp. petraea (Brassicaceae). We found variation in cumulative fitness, indicating significant adaptive differentiation among populations. Non-local populations did not exhibit higher fitness than the local population. Sites for reciprocal transplant experiments were located in Norway (alpine), Sweden (coastal) and Germany (continental). At all sites after one year, the local populations also had higher cumulative fitness, as quantified by survival combined with rosette area, than at least one of the non-local populations. At the Norwegian site, measurements were done for two additional years and fitness differences were found to persist. Fitness components contributing most to differences in cumulative fitness varied among sites. Relatively small rosette area combined with large number of inflorescences produced by German plants may reflect differentiation in life history. The results of the present study demonstrate that A. lyrata harbours considerable variation in several characters contributing to adaptive population differentiation. The wealth of genetic information available for this species makes A. lyrata a highly attractive system for examining also the functional and genetic basis of local adaptation in plants.