Restrictive cardiomyopathy is probably the least common of all cardiomyopathies, with a nonspecific clinical presentation and a frequently unknown cause. The concept of RCM has changed tremendously over time. Today it includes a large panel of disorders characterized by a non-hypertrophied, non-dilated cardiac phenotype and a restrictive ventricular filling pattern. Several unsuccessful attempts to define and classify cardiomyopathies have been made, but they all proved problematic due to the contradiction in terms and the overlap between classical patterns. Advances in disease pathology, genomics and molecular biology are emerging as the framework of a new revolutionary classification system, focused on the dynamic interaction between genotype and phenotype. In this context, RCM is evolving as a self-contained hemodynamic and pathophysiological concept, although questionable due to its uncertain practical utility.