Ambrosius Reiner (also known as Ambrosius Rainer) was a German composer active during the late Renaissance and early Baroque periods, primarily in the late 16th century. His work is associated with the genres of early polyphonic choral music and sacred compositions. Reiner is best known for his contributions to the development of motets and liturgical music, which were significant in the context of the Protestant Reformation. One of his notable works includes the collection of motets published in 1586, which showcases his skill in counterpoint and harmony. Although not as widely recognized as some of his contemporaries, Reiner's compositions contributed to the evolution of choral music during a transitional period in European music history. His style reflects the intricate polyphonic textures that characterized Renaissance music while also hinting at the emerging Baroque emphasis on melody and harmony. Reiner's impact on music is seen in his influence on subsequent composers who sought to blend the rich traditions of choral writing with the new stylistic approaches of the Baroque era, thus bridging the gap between these two significant musical periods.