The construction of Pichia pastoris expression strains and the general growth and manipulation of this yeast expression system are in many ways similar to those of bacterial expression systems, particularly Escherichia coli. Because of this, it is typically easy for researches experienced with bacterial systems to make the jump to this eukaryotic system. However, because the system is similar, users can be falsely fooled into assuming that the system is completely bacterial-like and may waste time and effort performing experiments that are unlikely to yield the desired results with this yeast. To aid in preventing P. pastoris users from falling into one or more or these traps, this introduction focuses directly on key ways that the P. pastoris expression system is different.