 Lactases are copper-containing enzymes that can catalyze the oxidation of a wide variety of substrates using molecular oxygen as the final electron acceptor. They are eco-friendly, versatile bio-catalysts with many applications in industry, including food additives and beverages, biomedical diagnosis, furniture construction, biofuels, and bioremediation. Recent research has focused on developing implantable biosensors and biofuel cells based on lactase activity, as well as its potential use in enzymatic remediation of contaminated sites. This article was authored by Diana M. Mait and Miguel Alcalde.