C-reactive protein (CRP) is an acute phase protein that plays a major role in the regulation of the inflammatory response. It activates the classical complement pathway in a controlled fashion, enhancing the capacity for defence against bacterial infections. It promotes the regulation of MPhi activity through FcgammaR, and is associated with the clearance of apo cells and nuclear antigen, thus becoming a protective molecule against pathogenic autoimmune responses in general, and systemic lupus erythematosus in particular. CRP is also associated with atherosclerosis, both in the general population and in different auto-immune conditions. It plays a double role as a biomarker for vascular risk and as an independent risk factor as it can also perpetuate the inflammatory response. Its multi-task behaviour makes it a pivotal structure both in the comprehension of the pathogenesis of auto-immune and inflammatory responses as well as an important tool in the clinical management of patients.