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The chromosomal passenger proteins display a distinctive pattern of localisation through mitosis. In human cells this group currently comprises six proteins; Survivin, Aurora-B, Aurora-C, INCENP, TD-60 and Borealin. To try and understand the functions of INCENP, various truncations have been expressed. The N-terminus of INCENP has previously been shown to be essential for targeting to the centromere when expressed ectopically. I have carried out a yeast two-hybrid screen in order to identify proteins that interact with this region of INCENP. This screen identified a number of potential INCENP interactors. I have further analysed one of these proteins, FLJ14346. I have shown that it has a dynamic localisation during mitosis, associating with the spindle poles and spindle microtubules, the midbody during cytokinesis and then with the centrosomes during interphase. This protein binds INCENP, Borealin and TD-60. The interaction with TD-60 is of particular interest since no direct interaction has yet been shown between TD-60 and the other passenger proteins. In a separate study, performed as a collaboration between several labs, we characterised the role of INCENP in male meiosis in Drosophila melanogaster. This study revealed that INCENP was required for the maintenance of sister chromatid cohesion in meiosis. INCENP and Aurora-B partially colocalised with MEI-S332, a protein that is known to be required for the maintenance of sister chromatid cohesion in meiosis. My data presented in this thesis shows that INCENP binds MEI-S332 in vitro. We show that MEI-S332 is phosphorylated by Aurora-B in vitro and that mutation of the Aurora-B phosphorylation site leads to unstable association of MEI-S332 with the centromere.