Binaries composed of a white dwarf and a main-sequence star are a frequent outcome of binary evolution. If the separation between the two components is small matter flows from the main-sequence star onto the white dwarf. Such accreting systems are called cataclysmic variables (CVs). Very little is known about CVs in which the donor is a very low-mass star or a brown dwarf (spectral type L), i.e. it belongs to the class of ultracool dwarfs (see topic "Magnetic activity"). We work on the identification and characterisation of such systems through optical and X-ray observations.
