Abstract Passive Brain-Computer interfaces (passive BCI), also named implicit BCI, provide information from user mental activity to a computerized application without the need for the user to control his brain activity. Passive BCI seem particularly relevant in the context of music creation where they can provide novel information to adapt the music creation process (e.g. user mental concentration state to adapt the music tempo). In this chapter we present an overview of the use of passive BCI in different contexts.We describe how passive BCI are used, and the commonly employed signal processing schemes.