Klaus Robert Mueller Brain Computer Interfacing makes use of brain signals for the control of objects (e.g., wheel chairs), spelling, computer gaming, and other applications. This talk will provide a brief overview of current Brain Computer Interface technology. In particular, it will show the wealth, complexity and difficulties of the data available. The challenge is enormous: Neuro-electric activities provide a high dimensional, very strongly noise contaminated data stream. This data stream needs to be processed and decoded accurately and in real time, so that (metaphorically speaking) thoughts can be translated into actions. The talk will then report in more detail about the Berlin Brain Computer Interface that is based on Electroencephalography (EEG) signals, and take the audience all the way through the processing chain. Finally, Brain Computer Interfacing application examples ranging from clinical studies where ‘locked-in’ patients achieve communication to non-clinical applications where, for instance, complex cognitive states while driving a car are analyzed, will be presented.