Singing con bocca chiusa, with closed mouth, is a phenomenon that appears both in solo and choral literature. This thesis would like to shed more light on the phenomenon and explain its occurrence by using literature examples. In addition to its special timbre, bocca chiusa also offers numerous pedagogical advantages and can be used both in individual work with voices and in choir practise. This thesis also tries to illustrate that bocca chiusa is a multifaceted register and wants to show its different extended possibilities.