The topic of bilingualism and cognition has been well debated in recent years, particularly in relation to cognitive gains as a consequence of speaking multiple languages. There is a long established belief that the experience of learning a second language, be it simultaneously with another from birth or later in childhood/early adulthood, leads to advantages in executive functioning (Bialystok, 2005). However, it has also been proposed that the cognitive advantages seen previously in studies with bilingual populations are not clear cut and that other factors may be influencing the results (Gathercole et al., 2014; Hilchey and Klein, 2011; Paap and Greenberg, 2013). The studies presented in this thesis addressed bilingualism and its effects on cognition in both infant and young adult participants taken from the North Wales area and the Bangor University student population. The infant study addressed semantic priming and working memory, and the young adult studies addressed response inhibition and suppression. The results of these studies proved inconclusive and suggest that the topic of bilingualism and cognition is a complex one. There are many factors that need to be considered and controlled in future studies with bilingual populations including age of acquisition, amount of exposure, language dominance, socioeconomic status, proficiency, and general intelligence. The experience of acquiring multiple languages places demands on cognitive load, which perhaps in turn results in advantages on tasks requiring executive functioning. These advantages may also be gained from other experiences that place demands on cognitive load such as musical training, video gaming, and dancing. Experiences shape the brain and the process of unraveling which experiences lead to these changes is a multifaceted process that needs to be prudently approached.