Staphylococcus aureus is a formidable pathogen and major challenge to human health. However, the bacterium is dichotomous and also acts as an asymptomatic coloniser. Given its ubiquity, every individual has been exposed to the bacterium, which may ‘tune’ the host immune system. This prior exposure potentially hampers the efficacy of anti-S. aureus vaccines, diminishing their protective effect. Conversely, by preserving its niche as a commensal coloniser, the bacterium simultaneously contributes to host defence through interbacterial competition and stimulation of host immune responses, potentially fending off pathogenic threats. This review examines how S. aureus shapes host immunity via infection and colonisation and explores how S. aureus-associated immune tuning can be both problematic and beneficial for the host.