My PhD project focuses on the population genetics of the Argentine ant (Linepithema humile), a highly invasive species. Originating from Argentina, L. humile has been introduced in many different countries with Mediterranean climates like Australia, Hawaii, Chile, France, etc. This species is considered throughout its introduced range as a human pest and is regarded as harmful to the indigenous flora and fauna. Its great invasion capacity can be explained by the particular social organisation found in introduced populations: unicoloniality. Unicolonial populations are characterised by supercolonies in which workers and queens mix freely among physically separated nests. The relatedness between nestmates is effectively zero and thus unicoloniality represents a paradox to kin selection theory. On the contrary, populations in Argentina are multicolonial and not invasive at all. The aim of my work is to understand how and why the social structure of the Argentine ant changes between native and introduced populations. I use genetical as well as behavioural approaches to compare native and introduced populations. Understanding of unicoloniality may help us to control invasive unicolonial species like Linepithema humile or Solenopsis invicta and would resolve one paradox of kin selection theory.