This study deals with the liturgical chant genre sequences sung all over Europe in the Middle Ages. The history of the sequence in Sweden, insufficiently known due to lack of sources, can now be more precisely described, thanks to numerous parchment fragments from dismantled books and used as covers for 16th century accounts, now in the Swedish National Archives. The investigation comprises two main parts: 1) a repertorial analysis with outlook on the European background and later Swedish liturgical traditions, 2) an inventory of all the fragmentary sources with a summary description and a reconstruction of codices in which scattered leaves are placed in their original order. Most fragments come from sequentiaries, graduals or missals dating to the 12th through the 15th century. The repertories often contain sequences from both the eastern and western European traditions, as well as some internationally distributed items of the new style, and a number of presumably Swedish compositions.