Memoria or the medieval remembrance of the dead is integral to our understanding of medieval society. However, memoria was not just a liturgical practice intended to lessen purgatorial suffering, but a ‘total social phenomenon’ that impacted every aspect of life. This thesis follows in the tradition of the German Memoriaforschung school, especially the concepts formulated by Otto Gerhard Oexle. These concepts are here particularly applied to memoria as a group phenomenon. A particular contention of this thesis is that memoria was socially constitutive and thus not only a vehicle to remember the past but a means to create and maintain social groups. Therefore this thesis takes the form of series of case studies drawn from late medieval Livonia (present day Latvia and Estonia) c. 1400-1525. The groups chosen –associations of the urban elites, non-elite brotherhoods, the clergy and the Livonian branch of the Teutonic Order – reflect both the strength of the surviving source material and the particular characteristics of the region. Each case study is considered through a series of research questions. How did memoria constitute and shape social relationships? How did memoria create and sustain groups? In what ways was memoria used for political purposes? How did groups use their past to maintain their identities in the present? What role did charity and the poor play? In addition to exploring the above themes, this thesis particularly argues that memoria was used to legitimize power by urban governments and by the Teutonic Order and the archbishops of Riga. This thesis also shows that memoria created the cultural memory of the Teutonic Order and the Rigan church. Memoria sustained the identities of urban elite groups and was essential to creating relationships between the urban elites and non-elite groups.