During his last years ethnohistorian Frank G. Speck turned to the study of Iroquois ceremonialism. This 1950 book investigates the religious rites of the Cayuga tribe, one of six in the Iroquois confederation that occupied upstate New York until the American Revolution. In the 1930s and the 1940s Frank Speck observed the Midwinter Ceremony, the Cayuga thanksgiving for the blessings of life and health, performed in long houses on the Six Nations Reserve in Ontario.  Collaborating with Alexander General (Deskáheh), the noted Cayuga chief, Speck describes vividly the rites and dances giving thanks to all spiritual entities. Of special interest are the medicine societies that not only prescribed herbs but used powerfully evocative masks in treating the underlying causes of sickness. In a new introduction, William N. Fenton discusses Speck’s distinguished career.