Our bodies are built from around 100 trillion individual cells, each of which contains 46 chromosomes that carry our genetic material. This enormous number of cells originates from a single cell that is the product of fertilization of an egg with a sperm. Thus, cell division is one of the most fundamental processes in the living world. At the onset of division the cell assembles the mitotic spindle, a fascinating and complex micro-machine made of microtubules and the accompanying proteins. The microtubules move the chromosomes around and finally line them up in the middle of the spindle. When all chromosomes are ready, sister chromatids are moved apart towards the opposite spindle poles. The central question in this field of research is how the mitotic spindle manages to divide chromosomes into two equal sets without errors. Understanding how proper chromosome segregation is achieved in cells and how it is controlled will help to identify new strategies for prevention and treatment of diseases such as cancer and genetic disorders caused by chromosome segregation errors. By taking an interdisciplinary approach, in which we combine cell and molecular biology, molecular genetics, cutting-edge microscopy, laser microsurgery, computer science and theoretical physics, my group explores how the mitotic spindle self-assembles and how forces that move the chromosomes are generated.