Who wrote it?

Over time, Pessoa's editorial plans for the Book have changed, including the authorship of the texts. Vicente Guedes first, and Bernardo Soares later, were the two characters created by Fernando Pessoa to be the authors of the work. But there is a difference between them: Vicente Guedes is a heteronym, Bernardo Soares is a semi-heteronym.

The texts written until 1915 are signed by Fernando Pessoa, from then on and until 1920 by Vicente Guedes. This is the phase of the long texts (the "Grand Excerpts"), inspired by the literary currents of Symbolism and the Decadent movement. 

According to known data, Fernando Pessoa interrupted the writing of the Book of Disquiet between 1920 and 1929.

The texts for the Book written from 1929 onwards are attributed to "Bernardo Soares, assistant bookkeeper in the city of Lisbon", who lives and works in Rua dos Douradores. They have a new, diaristic and confessional tone, and constitute most of the Book’s length. Bernardo Soares occupies the role of narrator-author of the Book of Disquiet.

There are also unattributed fragments, and it is not clear whether they were really destined for the Book. The most famous example of this type of difficulties is the fragment where, at the top, a note can be read: "Álvaro de Campos (?) or Book of Disquiet (or something else)".