The thesis aims to elucidate the process of designing interactive systems for musical performance that combine software and hardware in an intuitive and elegant fashion. The original contribution to knowledge consists of: (1) a critical assessment of recent trends in digital musical instrument design, (2) a descriptive model of interaction design for the digital musician and (3) a highly customisable multi-touch performance system that was designed in accordance with the model. Digital musical instruments are composed of a separate control interface and a sound generation system that exchange information. When designing the way in which a digital musical instrument responds to the actions of a performer, we are creating a layer of interactive behaviour that is abstracted from the physical controls. Often, the structure of this layer depends heavily upon: 1. The accepted design conventions of the hardware in use 2. Established musical systems, acoustic or digital 3. The physical configuration of the hardware devices and the grouping of controls that such configuration suggests This thesis proposes an alternate way to approach the design of digital musical instrument behaviour – examining the implicit characteristics of its composite devices. When we separate the conversational ability of a particular sensor type from its hardware body, we can look in a new way at the actual communication tools at the heart of the device. We can subsequently combine these separate pieces using a series of generic interaction strategies in order to create rich interactive experiences that are not immediately obvious or directly inspired by the physical properties of the hardware. This research ultimately aims to enhance and clarify the existing toolkit of interaction design for the digital musician.