Following the definition of ‘interior monologue’ (IM) given by Edouard Dujardin (1931), this paper analysed a corpus of novels (by Schnitzler, Joyce, Dostoevsky, Pirandello) in which this literary technique is used. It discovered that, although one of the conventional meanings of monologue is ‘discourse with one voice’, Ims reveal intrinsic dialogism among different voices. These voices come both from different ‘parts’ of the speaker and from others (imagined, internalized people). In this sense, Ims are polyphonic. The paper focuses on the linguistic and communicative forms of Ims, on how people speak to themselves. The method used consists, mainly, of a qualitative, structural linguistic analysis. Passages taken from the corpus explain how polyphony works in Ims.