Homocysteine, an "old-new" risk factor for cardiovascular diseases, plays also a role in numerous pathological conditions. Although it is not completely clarified if it a causal factor or only a biomarker, the interest in homocysteine is still high. The correct approach to the patient with hyperhomocysteinemia represents a challenge. The book attempts to present relevant aspects of the correlations between hyperhomocysteinemia and different diseases as well as the therapeutical solutions.