Hallucinations are often considered a sign of psychotic illness, but are also common in other diagnostic groups and individuals without mental health problems. This thesis uses Perceptual Control Theory (PCT), a cybernetic model which explains behaviour and cognition in terms of control processes regulating ongoing perception according to internally represented goals, as a theoretical framework to understand hallucinations. First, a theoretical/conceptual paper (Paper 1) examines how PCT provides an integrated account of (i) the mechanisms responsible for the formation of hallucinations, (ii) their phenomenological heterogeneity, (iii) the interaction between these mechanisms and environmental factors that might contribute to the formation of hallucinations, and (iv) the processes leading to different affective reactions to hallucinatory experiences (e.g. distress). The main implications of this model are discussed in the context of pertinent theoretical and empirical literature, and relevant clinical and research implications are considered.Second, this thesis includes an empirical investigation (Paper 2) examining two PCT-informed hypotheses in a cross-section of 22 clinical and 18 non-clinical individuals with auditory verbal hallucinations ("hearing voices"), namely (i) that the content of voices will be thematically linked to the participants' personal goals, and (ii) that affective reactions to voices will depend on the extent to which voices facilitate and/or interfere with important personal goals. The analysis revealed that 82.5% of participants reported voices that thematically matched at least one of their reported goals. As predicted, affective reactions to voices were strongly associated with measures of interference and facilitation of goals, even when controlling for important covariates (e.g. participants' history of mental health difficulties; voices' content, frequency and duration).Finally, a critical evaluation is provided (Paper 3), where the methodological strengths and limitations of the work presented in the present thesis are discussed with the aim to reflect on the research process, and inform future investigations into the topics considered in this thesis.