The last century has seen an incredible leap in human medicine, which has led to an increased life expectancy spanning over all age groups. Despite this development of modern medicine some patient groups do not have any proper treatment except for artificially prolonged life. One such group of patients suffer from neurodegenerative illnesses or spinal chord injuries resulting in a state of complete locked in syndrome (CLiS).The last couple of decades have on the other hand seen the emergence of a new promising technology in such context, namely the brain computer interface (BCI.) This thesis gives a extensive survey of the BCI field in a biomedical context and also highlights two BCI systems based on scalp EEG recordings. Even though BCI technology is mainly limited to research settings so far, it has great perspectives for the future - both for improving daily life in clinically targeted groups of patients, in cognitive neuroscience, and entertainment and gaming activities.