The invention is directed to polypeptides having a glucosidase activity, including an alpha-glucosidase activity, polynucleotides encoding the polypeptides, and methods for making and using these polynucleotides and polypeptides. In one aspect, the polypeptides of the invention are used as alpha-glucosidases to catalyze the hydrolysis of starch into sugars, e.g., to convert liquefied starch to glucose. In one aspect, the polypeptides of the invention can catalyze the hydrolysis of both alpha-(1,4) and alpha-(1,6) glucose linkages. In one aspect, the polypeptides of the invention can catalyze the hydrolysis of both malto-oligosaccharides and liquefied starch.