Emulsions comprising a water insoluble or semi-soluble silane or mixtures of such silanes have been found useful when used alone or formulated into aqueous primer systems to improve the adhesion of sealants, adhesives or coatings to a variety of substrates. These aqueous primers are suitable for both inorganic and organic substrates having either porous or non-porous surfaces. In many cases they have been found to outperform solvent based primers. Primers of this type can be used with a variety of waterborne or solvent based sealants, adhesives or coatings including acrylic or polyurethane latexes, high solid polyurethanes, epoxies and silicones. When used with waterborne systems, it is not necessary to wait for the primer to dry before application of the sealant, adhesive or coating.