The signals captured by the hearing aid microphone(s) are typically a mixture of multiple simultaneous source signals : (several human) speakers, music coming from a radio, background noises, ... can be heard at the same time, as in a cocktail party. Some of these sound sources are of interest to the hearing aid or cochlear implant user, others aren't. Blind source separation is a technique that can segregate the source signals from several observed mixtures, i.e. it can recover the original unmixed source signals from the microphone signals. Blind source separation appears to be most effective against directional noise sources. In this project blind source separation is applied to bilateral hearing aids, i.e. microphone signals from both the left and the right hearing aid are processed simultaneously.