Singing combines speech and music – two activities common and perhaps fundamental to almost all human cultures. Singing involves the coordinated, precise and subtle control of breath, sound production in the larynx, articulation of the vocal tract – and their interactions. This chapter begins with an introduction to the fundamental process of phonation: the interaction between laryngeal airflow and the vibration of the vocal folds and nearby tissues that give rise to voiced sounds. Different biomechanical configurations of the larynx, known as laryngeal mechanisms or laryngeal registers, induce various modes of vibration and help to cover the wide range of frequencies associated with singing. The nonlinearity of their vibration produces the harmonic richness of the voice spectrum. The chapter then introduces the acoustical properties of the vocal tract and its resonances, which act as a filter that selectively enhances the output power of some of the frequencies in the voice. It then discusses the interactions between the vocal folds and the acoustic waves in the vocal tract. Finally, it discusses singing and the techniques of resonance tuning: the ways whereby singers adjust their tract resonances to produce a louder, sometimes more stable voice with less effort.