Encyclopedias are great for:
Medieval Scandinavia: An Encyclopedia. 1993. (Olin Reference DL30 .M48+ and Kroch Rare Reference). Articles vary in length but all are accompanied by bibliographies.
Dictionary of the Middle Ages. 12 vols. 1982-1988. (Olin Reference D 114 D55+; also Uris Reference) Articles cover roughly the years 500-1500 A.D. in the lands of the Latin West, the Slavic world, Asia Minor, the lands of the Caliphate in the East, and the Muslim-Christian areas of North Africa. Some entries are only of definition length (e.g. Avignon), but others are more historical and lengthy (e.g. Byzantine Empire, Constantine I, Arms and Armor). Bibliographies are mostly in English.
Medieval Archaeology : an Encyclopedia. 2001. (Olin Reference D125.M42x 2001+) A substantive up-to-date encyclopedia of medieval archaeology, with entries for sites (Sutton Hoo, e.g.), areas (Pre-Viking Scandinavia), ethnic/culture groups (Vikings, Visigoths), artifacts (Stoneware) and activities (Hunting, Cloth-making).
The Catholic encyclopedia and The New Catholic Encyclopedia Beyond the subject of Catholicism to include science, literature, art and civilization. Articles sometimes include bibliography of primary and secondary sources.
The Wiley Blackwell Encyclopedia of Anglo-Saxon England. 2nd ed. People, places, social groups. Most articles contain concise bibliographies.
Medieval England: An Encyclopedia. 1998.(Olin Reference DA 129 .M43x 1998) Articles vary in length but all are accompanied by bibliographies.
Medieval Ireland : an encyclopedia. 2005. (Olin Library Reference DA933 .M43 2005 +) Articles vary in length but all are accompanied by bibliographies.
Ancient Europe 8000 B.C.--A.D. 1000: encyclopedia of the Barbarian world. 2004. Two volumes. (Olin Library Reference D62 .A52x 2004+)
Encyclopedia of barbarian Europe: society in transformation. 2003. (Olin Library Reference D135 .F73x 2003+)
The Oxford Companion to United States history. Oxford University Press, 2001.
Dictionary of American history. A classic ten volume encyclopedia.
Encyclopedia of American Social History. 3 vols. New York: Scribner's, 1992. (Olin Reference HN 57 .E56 1992).
Encyclopedia of the United States in the Nineteenth Century. 3 vols. New York: Scribner's, 2001. Olin Library Reference E169.1 .E626x 2001
St. James Encyclopedia of Popular Culture. 5 vols. Detroit, MI: St. James Press, c2000. (Olin Reference E 169.1 S764x 2000) Five volumes.
Encyclopedia of the United States in the Twentieth Century. 4 vols. New York: Charles Scribner's Sons, 1996. (Olin Reference E740.7 .E56 1996).