astroML is split into two components. The core astroML library is written in python only, and is designed to be very easy to install for any users, even those who don't have a working C or fortran compiler. A companion library, astroML_addons, can be optionally installed for increased performance on certain algorithms. Every algorithm in astroML_addons has a pure python counterpart in the core astroML implementation, but the astroML_addons library contains faster and more efficient implementations in compiled code. Furthermore, if astroML_addons is installed on your system, the core astroML library will import and use the faster routines by default.