Medieval and Renaissance Studies 

• Dictionary of the Middle Ages. General Reference: D 114. D51. 1982 Q
  
• Encyclopedia of the Middle Ages. General Reference: CB351.E53 2000 Q
• Encyclopedia of the Renaissance General Reference: CB 361.E52 1999 Q
  
• Europe: encyclopedia of the early modern world.
  General Reference: D 209 .E97
• There are several encyclopedias of individual countries in General Reference: England, France, Germany, Iberia, Ireland, Italy, Scandinavia
  
• Die deutsche Literatur des Mittelalters : Verfasserlexikon.
  A 10-volume encyclopedia of medieval German literature.
  D Level : Z 2230 .D47 1978
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Medieval and Renaissance manuscripts in the US and Canada. De Ricci. 2 volumes plus Supplement
General Reference Z 6620 .U5R4

CORSAIR: the online research resource of the Pierpont Morgan Library, one of the finest collections of medieval manuscripts in North America.

Catalogue général de manuscrits français. Bibliothèque Nationale.
D Level: Z 6621 .P22 F8

Index to the Manuscripts in the British Library. 10 volumes
D Level: Z 6621 .B84A5 1984 QUARTO

Catalogue of Digitized Medieval Manuscripts

Bibliothèque Nationale de France: archives et manuscrits.

Manuscripta Mediaevalia: major research site for medieval manuscripts in German-speaking countries. Includes digitized versions of manuscript catalogs and a Handschriftendatenbank

Inventari dei manoscritti delle biblioteche d'Italia.
104-volumes. Arranged by region, and then by library. D Level: Z 6620 .I8 M4

Inventario general de manuscritos de la Biblioteca Nacional.
15 volumes D Level: Z 6621 .M197

• Medieval Studies: a bibliographical guide. Start here!
  General Reference CB 351 .Z9C76

• Medieval studies: an introduction.
  General Reference : D 116 .M4

• Manuel bibliographique de la littérature française du Moyen Age. R. Bossuat.
  An essential tool.
  General Reference: PQ 15 1.B65 1971
  

• Bibliografía de la literature hispánica. J. Simón Diaz
  The indispensable bibliography for Spanish literature: medieval and Golden Age
  General Reference: Z 2691 .S5
  

• Grundriss zur Geschichte der deutschen Dichtung (Goedeke) : Das Mittelalter (Bd I : Dichtung vom Beginn bis 1515).
  The single most important bibliographic tool for German literature up to 1830
  D Level Blue Labels: PT 85 .G7 1975 (Index PT 85 .G7 1884)