Part I of this document, being what I am, theorises an identity for the composer, and examines precepts and influences in my own development. Part II, doing what I do, discusses each of the six works presented in the portfolio. A set of appendices, presenting diagrams and other supporting material, is included as a separate volume. Chapter 1, what do composers do?, introduces the semiotic theory of Charles Sanders Peirce, detailing his categorisation of different sign types and function. Examples in relation to an electroacoustic piece connect to an account of Molino's and Nattiez' "tripartition" poiesis-trace-esthesis, which is used to frame an analysis of what a composer can know in relation to their audience and, via Peirce, is re-scaled to operate at micro and macro levels. Drawing on Peirce and Nattiez, I construct a definition for "music", as sound which is either created or heard (whether or not made that way) to have organisation perceived through certain types of non-linguistic sign function. A series of postulates on the nature of art in the postmodern world lead to the proposition that a composer is someone who tries to make music that is art. Chapter 2, being this composer, introduces themes central to my doctoral composition activity, and relates them to a set of problems I see as facing (or dividing) composers and audiences. I give an acc ount of my learning experiences in theUSA in relationto the UK. An examination of the traditional principles of counterpoint is extrapolated to the proposal for a generalised counterpoint, involving the cross-setting of "energy profiles" within a semiotic space elucidated by Peirce's sign classifications. I discuss the roles of signalling, physicality and spatialised sound in capturing and sustaining audience attention, and present a group of conceptual and practical crossovers between acoustic and electroacoustic technique. An apparatus for compositional "quality control" is discussed in relation to the Nattiez tripartition. The chapter closes with a commentary on musicology's sometimes-ignorance of developments in other areas of critical thought such as literary theory, and a reassessmen tof the role of this thesis document. Introducing the portfolio, Chapter 3 discusses an extended tapework, Three Friends, which takes recordings of acoustic improvisations as "musical" anchors for a referential play, increasingly mobile in the successive movements. The finale brings together the three sources in a virtual chamber music. The piece has strong formal direction,which is presented as a metaphor of my compositional development over the corresponding period. Functional pitch and harmonic structures support behaviours only possible in the electroacoustic medium.The work plays with electroacoustic tropes and introduceshumour. An assessmen tof the first performances encourages re-affirmation of tape composition's vitality. In Chapter 4, an analysis of the dialectical interaction between performance showmanship and musical substance leads to a theory of the virtuoso performer as musicalcyborg. Aesthetic challenges especially face the composer/performer of new electronic instruments; the violin's density of cultural referents enable a violin-like instrument to solve some of these challenges.The conceptual and technical evolution of such an instrument,the "funny fiddle", and realisation of a first concert work, Gipsy fugue, are discussed in detail. Examination of the relationship between compositional intent, practical possibility, and an emphasis on evolutionary "satisficed" technology, together with assessment of thework's reception,inform discussion of future developments. Chapter 5 describes a site-specific interactive installation, who's in charge?, designed to "activate" audience members arriving for a concert. The technical apparatus is borrowed from the funny-fiddle system, with the addition of slides projected to appear as posters or direction signals. The elements of the installation are susceptible to various levels of semiotic registration. Ethical responsibilities are discussed in relation to the tacit audience-manipulation. Chapter 6 introduces Teen, a piece for brass quintet and percussion that sets four short abstract texts written when I was a teenager. Subjective and analytical modes of text-setting interact with musico-formal design. The music's contextual relationship to its audience is discussed, as are the difficulties of performing and recording a work that is deceptively demanding. Chapter 7 asks what is song? and discusses the interaction of semiotic behaviours in music (as defined earlier) and text. The texts of New Yorker Songs come from early years of The New Yorker magazine. Saraband makes a linear, cinematic setting of a narrative but multivocal poem. A freely atonal musical language, diatonically inflected, but equally concerned with spectral and physical space, is propelled by the speech rhythm. Aspects of the setting are discussed in semiotic terms. Line uses and fragments a shorter text, setting it through formal structures at the background and middleground level, with foreground concerns for gesture and texture. This is examined through Emmerson's(electroacoustically-conceived) "language grid". Lastly, the computation-aided realisation of musical texture is discussed. Chapter 8 presents Chaconnes, for violin and electronic sounds. Its motivations are similar to those of the funny-fiddle project, but with a complementary solution. Precomposed electronic elements are triggered in chamber-music dialogue with the unamplified acoustic violinist. The piece downplays extra-musical reference, seeking an internally-directed language "natural" to the acoustic instrument. Analysis of a Bach model introduces discussion of form and rhetoric. This chapter emphasises strategies for pitch structuration. A custom playback-tool for the electronic sounds streamlines the separation of musical composition and technical development, and provides an efficient performance environment.