Baron Carl Nils Daniel Bildt (15 March 1850 – 26 January 1931) was a Swedish diplomat and historian.

[1] After a law degree from Uppsala and holding various lower-ranking diplomatic posts in London, Paris, Washington D.C., Berlin and Vienna, and as state secretary for foreign affairs, he was appointed Swedish envoy to Rome in 1889.

[2] Throughout his years in Italy, Bildt published a number of works on Italian or Italo-Swedish topics, starting with his Anteckningar från Italien av en svensk diplomat ("Notes from Italy by a Swedish diplomat"), with historical descriptions of a number of Italian towns.

He wrote essays on earlier Swedish visits to Italy, such as the one by King Gustav III in 1783, but his main focus was on Saint Bridget of Sweden who spent her last years in Rome and Queen Christina, who settled there after abdicating from the Swedish throne (1654) and converting to Roman Catholicism (1655).

With his excellent connections in Rome, Bildt was able to access until-then unused sources in Roman public and private archives and published articles on many previously unknown episodes in and aspects of Christina's later life.