In the post genomic era and with the rapid developments in the field of Systems Biology there is an increased demand for ‘virtual cells’. Here a number of initiatives towards such cells are discussed with an emphasis on how they differ in aims and functionalities. Then one of the initiatives is described in much more detail. This ‘silicon cell’ initiative aims at producing computer replica of living organisms, with an initial focus on individual cells and pathways therein. Once journal-refereed, the replica are put onto a dedicated website, such that they can be interrogated by the worldwide scientific community. The replicas enable experimentation in silico, which may advance drug design, biotechnology and teaching. A major challenge will be the quality control and improvement, and the coupling of the replica of parts of living cells into replica of larger parts.