This chapter is concerned with nuclear division of mitosis in a typical vertebrate cell. It shows that spindle microtubules, gaining access to the nuclear compartment, attach to chromosomal kinetochores. The chapter examines that in order to account for the erratic movements of chromosomes at metaphase, the kinetochore attachment must be of a special kind. During mitosis in plant and animal cells, populations of microtubules grow, attach to chromosomes, and maneuver them with amazing precision into two newly created nuclei. Mitosis itself is traditionally subdivided into a sequence of stages according to the behavior of the chromosomes, the principal stages being prophase, metaphase, anaphase, and telophase. Mitosis is not the only event in which chromosomes are moved within the cell. Sexual reproduction also requires extensive rearrangements of the genetic material under the guidance of microtubules.