Our inner space is furnished, and sometimes even stuffed, with verbal material. The nature of inner language has long been under the careful scrutiny of scholars, philosophers and writers, through the practice of introspection. The use of recent experimental methods in the field of cognitive neuroscience provides a new window of insight into the format, properties, qualities and mechanisms of inner language. Gathering findings from introspection and empirical works, this article first assesses the proportion of language in our inner space. Several variants of inner language are then described, including wilful vs spontaneous instances, condensed vs expanded forms, silent vocalisation during reading or writing, contained vs ruminative occurrences, and self-controlled vs hallucinatory cases. The nature of these variants and their embodied multisensory qualities are examined. Finally, a neurocognitive model of the production of inner language is drawn, in the framework of predictive control, speculating on the neural mechanisms that underlie one of the most significant components of our inner space.