For a long time it has been known that in the 16th century the Swiss mathematician Jost Bürgi found a new method for calculating sines, but no information about the details has been available. Recently a manuscript written by Bürgi himself has come to light in which he explains his algorithm. It is totally different from the traditional procedure which was used until the 17th century. In the first part of the article the standard method is explained which was rooted in Greek antiquity with Ptolemy's computation of chords and which was used in the Arabic-Islamic tradition and in the Western European Middle Ages for calculating chords as well as sines. The main part of the article deals with Bürgi's way. By only using additions and halving, his procedure is elementary and it converges quickly. Bürgi does not explain why his method is correct, but in the last part of the article a modern proof for the correctness of his algorithm is provided.