Marketers and brands continuously search for innovative methods to reach target segments in the most effective way. Social media is one of the fastest evolving communication tools nowadays, exercising a considerable impact on Marketing. Social Influencer Marketing is one of the latest tools combining these elements. The pursued objective of this thesis is understanding the impact of Social Influencers through Instagram on the buying behaviour of lifestyle products of young Belgian women. Additionally, we do research on elements as attitude, credibility, persuasion attempt and sponsorship disclosure of Influencer Marketing through Instagram. The methodological approach chosen is a positive approach consisted of two phases. The first is a literature review followed by a qualitative study. During the literature review, we provide you with a theoretical context on Influencer Marketing, as well as on consumer purchase behaviour. Subsequently, we interviewed eight Instagram Influencers, one company applying Influencer Marketing, and eleven young Belgian potential consumers during the qualitative phase. The second phase consists in a quantitative study with the objective to verify a set of research hypotheses. We drew up six hypotheses that we tested with the help of an online survey. ; Master [60] en sciences de gestion (Mons), Université catholique de Louvain, 2018