The pubmed search term “pastoris[Title] AND (express[Title] OR produced[Title] OR expression[Title] OR production[Title]) ” yielded 877 hits in December 2008, dated from 1987 to 2009. At the same time, the search term “pastoris[Title] AND (bioreactor[Title] OR fed-batch[Title] OR continuous[Title] OR fermentations[Title] OR large-scale[Title] OR fermentation[Title] OR pilot[Title]) ” returned 92 hits –published between 1990 and 2009. This analysis is somewhat superficial and ostentatious, but it suggests that the majority of researchers publishing on Pichia use it as a tool for rather than an object of their work. This is not to say that the majority should change their focus, but in fact researchers sometimes face difficulties when the need to obtain useful amounts of a target protein produced in Pichia calls for scale-up from the benchtop protocols to a bioreactor-based process. This chapter attempts to provide a reliable protocol for AOX1 -driven bioreactor production of secreted scFvs or other proteins.