A simple tool to quantify the amount of transmission of an infectious disease of interest occurring within and between population groups. 'bumblebee' uses counts of observed directed transmission pairs, identified phylogenetically from deep-sequence data or from epidemiological contacts, to quantify transmission flows within and between population groups accounting for sampling heterogeneity. Population groups might include: geographical areas (e.g. communities, regions), demographic groups (e.g. age, gender) or arms of a randomized clinical trial. See the 'bumblebee' website for statistical theory, documentation and examples < https://magosil86.github.io/bumblebee/>.