The Stasi first began keeping tabs on Grass, arguably Germany's best-known post-war writer, in 1961 when he wrote an open letter attacking the construction of the Berlin Wall by the communist German Democratic Republic (GDR), the book shows.
"Grass was unbelievably well known in the GDR. His books were banned for decades, but everybody knew him. He often visited the GDR and people would say, 'That's Grass'," said Kai Schlüter, the new book's author.
But when Grass, now 82, whose best-known book "The Tin Drum" came out in 1959, visited East Germany to give readings, the Stasi successfully followed his every move, giving him the code name "Bolzen," or "bolt."
"Grass was completely surrounded by spies when he came to the GDR. All his official interlocutors were IMs (unofficial informants), all of them," said Schlüter, who went through over 2,000 Stasi files to compile his book.
"Whether they were from writers' associations, publishers' representatives, state representatives, theatre people ... he was completely surrounded. This really surprised me," Schlüter told Radio Bremen in November.
"From the moment he crossed from West Berlin at the Friedrichstraße checkpoint until he left again, he was monitored the whole time. He says he never noticed."
These informers would tell a Stasi officer what Grass said and did, which would then be meticulously recorded in documents that were opened to the public after German unification in 1990.
Schlüter said that he was of particular interest to the Stasi because unlike other "easy ideological targets" like West German chancellor Konrad Adenauer, Grass, as a supporter of the centre-left Social Democratic Party, was seen as a more insidious threat.
The book, Günter Grass im Visier - Die Stasi-Akte (Günter Grass in the Cross Hairs - the Stasi Files), is published by Christoph Links Verlag.