The second half of the nineties saw the start of a wave of immigration to Spain of an intensity that has brought about far-reaching changes in Spain's demographics, society and economy. Inmigrants have come to represent 16% of the active population, this fi gure surpassing most of the countries that traditionally have more foreign residents. The bulk of this migratory fl ow has primarily been attracted by the opportunities offered by an expanding labour market. This paper focuses on the impact of this phenomenon on the labour market, through available statistics and studies, and reaches three broad conclusions. First, the infl ux of foreigners has helped to enhance the growth cycle of the Spanish economy at the expense of growth in the apparent productivity of labour. Second, despite the size of this phenomenon, the great wave of immigration does not seem to have altered the parameters within which the labour market operates. Finally, the high unemployment among foreigners as a result of the economic downturn threatens to continue for some time.