The site of microtubule attachment to the chromosome is the kinetochore, a complex of over 60 proteins assembled at a specific site on the chromosome, the centromere. Almost every kinetochore protein identified in yeast is conserved through humans and the organization of the kinetochore in yeast may serve as the fundamental unit of attachment. More recently we have become interested in the role of two different classes of ATP binding proteins, cohesions (Smc3, Scc1) and chromatin remodeling factors (Cac1, Hir1, Rdh54) in the structural organization of the kinetochore and their contribution to the fidelity of chromosome segregation.,The site of microtubule attachment to the chromosome is the kinetochore, a complex of over 60 proteins assembled at a specific site on the chromosome, the centromere. Almost every kinetochore protein identified in yeast is conserved through humans and the organization of the kinetochore in yeast may serve as the fundamental unit of attachment. More recently we have become interested in the role of two different classes of ATP binding proteins, cohesions (Smc3, Scc1) and chromatin remodeling factors (Cac1, Hir1, Rdh54) in the structural organization of the kinetochore and their contribution to the fidelity of chromosome segregation.