Abstract: A device for composing and arranging music comprising a sensor part and a plurality of blocks which may be releasably connected to the sensor part. A distribution of blocks, each belonging to one of a number of sub-populations of blocks on the sensor part, represents a composition or arrangement comprising musical features being dependant upon the sub-population(s) and the position of the block(s). Further, a device for building an instrument using blocks having activating means for activating the musical features of the block(s). The device may be used as an educational toy being easy to use for e.g. children. The device may be connected to a computer and to a global computer network so as to enable the device to communicate with other similar devices.