The black hole binaries detected so far by the LIGO-Virgo Collaboration have been “clean" sources of gravitational waves, since the binary dynamics were solely determined by gravity. Next generation gravitational-wave detectors, such as LISA, will in addition be sensitive to a number of “dirty” sources, affected by matter and the environment. In this talk, I will analyse in some detail two examples of dirty sources. In the first example, I will consider black hole binaries located in active galactic nuclei (AGN binaries). In the LISA band, these binaries could be affected by a long list of environmental effects, from dynamical friction to accretion, from acceleration/Doppler to strong lensing. I will show that these effects will allow us to measure the properties of the AGN accretion disk as well as the supermassive black hole at its center, including its mass. In the second example, our focus will move onto an elusive class of galactic binaries, containing a white dwarf and a black hole. I will conclude by mentioning some ideas on how to use dirty gravitational-wave sources to probe cosmology and the nature of dark matter.