This book draws heavily on records of the former East German Ministry of State Security (MfS). Often, in its reports, the MfS used such general terms as der amerikanische Geheimdienst ('the American secret service'), not specifying which particular American agency was at work. Therefore, I can often be no more specific than to say 'an American service'.
All the primary documents referred to in the footnotes are held in the National Archives in London (formerly the Public Record Office), unless otherwise stated. All documents whose citation begins with 'MfS' are held in the Zentralarchiv of the Bundesbeauftragte für die Unterlagen des Staatssicherheitsdienstes der ehemaligen Deutschen Demokratischen Republik (BStU, ZA).