This rapid realist review aims to explain how and why person-centred care (PCC) in primary care works (or not) among others for people with low health literacy skills and for people with a diverse ethnic and socioeconomic background, and to construct a middle-range programme theory (PT). The middle-range PT demonstrates that healthcare professionals (HCPs) should be trained and equipped with the knowledge and skills to communicate effectively (i.e. in easy-to-understand words, emphatically, checking whether the patient understands everything, listening attentively) tailored to the wishes, needs and possibilities of the patient, which may lead to higher satisfaction.