Despite increasing popularity and interest in contemporary a cappella, little research exists involving this genre of music making. In this study, I investigated how SIX, a professional contemporary a cappella group, utilizes a primary practice of aural arranging to create original, a cappella cover arrangements entirely by ear. From one initial question and use of classic grounded theory analysis, three questions emerged: what did SIX do, how did SIX carry out what they do, and what characterizes how SIX carries out what they do? The substantive theory of aural arranging and the substantive and formal theories of fluid leadership emerged from the data. The theory of aural arranging posits that SIX creates original cover arrangements by ear through the use of interactive activities initiated by application of task and social-emotional leadership. This substantive theory addresses the questions: what does SIX do and how does SIX carry out what they do? The theory of fluid leadership posits that SIX uses a form of horizontal leadership governed by five principles; 1) no single, primary leader, 2) leading in areas of strength, 3) accurate awareness of strengths, 4) a practice of unassuming leadership, and 5) the maintenance of a healthy relational climate. These substantive and formal theories address the question, what characterizes how SIX carries out what they do? Aural arranging and fluid leadership emerged from an environment of complex challenges wherein SIX established environments of safety and empowerment, promoting the sharing and utilization of musical and leadership thinking and knowing toward creation of an aural arrangement. Although the findings from this research are not generalizable given the single case study methodology, the theory of aural arranging presents a viable structure for creation of aural arrangements in other contemporary a cappella groups, and fluid leadership illustrates potential as a leadership model within small musical ensembles both within and beyond the formal music education classroom. The principles of fluid leadership may potentially be useful in dissimilar small groups traversing many disciplines. This study expands and enhances the current knowledge base related to contemporary a cappella, aural arranging, and leadership within small ensembles and groups.