This thesis traces the development of a number of mobile computer music systems and their use in ensemble percussion performances. The research is motivated by the challenges of working with laptop based computer music systems in ensemble situations. The aims were to develop elegant, portable, and flexible computer music tools, to make these tools accessible to other percussionists, and to discover the opportunities that they enable in performance practice.These aims have been explored through three musical projects for percussion and Apple's iOS devices: Nordlig Vinter, a suite of duo compositions; and two collaborative works, 3p3p and Snow Music developed together with two other percussionists.Articulated from a performer's perspective, this artistic research examines a number of software frameworks for developing mobile computer music applications. The development, rehearsal process and performances of the musical projects have been documented with video and audio recordings.An ethnographic investigation of this data has given insight into the limitations and affordances of mobile computer music devices in a variety of performance contexts. All of the projects implemented elegant computer music setups and the limited visual interfaces of the mobile devices demanded simple but clear interface design. In Snow Music in particular, "percussive" interaction with the mobile devices along with an improvised performance practice contributed to a collaborative development cycle. This process revealed some of the limits of expression with the computer sounds used and led to a very successful series of performance outcomes. / <p>Validerat; 20120614 (anonymous)</p>