Literature on bilingualism and cognition is characterised by a large amount of conflicting evidence. In some studies, bilinguals perform better then monolinguals on executive tasks involving inhibition, monitoring and switching but are slower on tasks of lexical processing. Other studies don’t find any significant effects and challenge the very existence of cognitive differences between monolinguals and bilinguals. This paper questions the assumption that different studies performed in different parts of the world should yield the same results. It is argued that the environment (in the widest sense of the word) in which an experiment is conducted can exert profound influence on its outcome. Against the background of the current debate about the replication crisis in science, the paper proposes that conflicting evidence is not a threat to the trustworthiness of scientific research but a sign of the health of a discipline and a welcome opportunity to identify new relevant variables.