The present invention relates to the expression of polypeptides using Yarrowia lipolytica, in particular the secretion of expressed polypeptides into either the extracellular space or the surface of the Y. lipolytica host cell wall. The invention also extends to the use of the polypeptides so expressed in biotechnological applications. The present invention provides an expression construct for the expression of polypeptides using at least a single Yarrowia lipolytica yeast cell, the expression construct having at least one expression cassette, the expression cassette including an acid extracellular protease secretion signal sequence and flanking zeta sequence recombination sites.