The Cellosaurus is a knowledge resource on cell lines. It attempts to describe all cell lines used in biomedical research. Its scope includes: Immortalized cell lines; naturally immortal cell lines (example: stem cell lines); finite life cell lines when those are distributed and used widely; vertebrate cell line with an emphasis on human, mouse and rat cell lines; and invertebrate (insects and ticks) cell lines. Its scope does not include primary cell lines (with the exception of the finite life cell lines described above) and plant cell lines.