Trypanosomatids possess a highly ordered array of sub-pellicular microtubules that restrict all vesicular traffic to the flagellar pocket (FP); a small invagination of the plasma membrane located at the base of the flagellum. Although the FP is not an adaptation to parasitism per se, it is without question a key pathogenicity feature that has enabled parasitic trypanosomatid species to exploit a diversity of host environments. In this chapter, we focus on the FP of the African trypanosome Trypanosoma brucei and consider recent advances in our understanding of the physical architecture of the FP and the dynamics of FP operation. We conclude with a brief discussion that the trypanosomatid FP represents an example of “extreme biology”, i.e. a normal but exaggerated example of the cell biology present at the flagellum base in proliferating flagellated eukaryotic cells.