Several observational and intervention studies have found an inverse association between the risk of cardiovascular disease and the consumption of polyphenol-rich foods and beverages such as cocoa, fruit and vegetables, tea, virgin olive oil and wine. We present here an overview of the latest research on the beneficial effect of dietary polyphenols on blood pressure, focusing on the development of urine biomarkers for an accurate estimation of polyphenol intake. Total polyphenols (TP) excreted in spot urine samples have been successfully used as a biomarker of the consumption, bioavailability and accumulation of TP in a cross-sectional clinical trial. In addition, we describe how the vasoprotective effect of dietary polyphenols has been related to their ability to increase endothelial synthesis of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF)-mediated responses.