A Lewis base is a chemical species that donates an electron pair to form a covalent bond with a Lewis acid. This interaction is part of the broader Lewis theory of acids and bases, which focuses on electron pair transfer rather than proton transfer, as seen in the Brønsted-Lowry theory. Common examples of Lewis bases include ammonia (NH₃) and water (H₂O), both of which have lone pairs of electrons available for donation. Lewis bases play a crucial role in various chemical reactions, including coordination chemistry and catalysis, by facilitating the formation of new bonds.