Encyclopedias and subject dictionaries are useful to get acquainted with your topic, to learn about good primary and secondary works on the topic, and to help broaden or narrow the topic.
Witch Hunts in Europe and America, an Encyclopedia, Reference BF 1584 .E9 B87 2003
Oxford Dictionary of the Middle Ages Main D 117 .O92 2010 v. 1-3
Greenwood Encyclopedia of Global Medieval Life and Culture Main CB 351 .G743 2009 v. 1-3
Covers the whole world during the period called medieval in Western Europe. v. 1 covers Europe and the Americas. V. 2 covers Africa and the Middle East. V. 3 covers Asia and Oceania. For each, there are: chronology, maps, overview and topical essays (historical overview, religion, economy, arts, society, science/technology, global ties), short entries for: people, ideas, events and terms, primary documents, and an appendix about dynasties of rulers.
Dictionary of the Middle Ages, Main D 114 .D5 1982, v. 1-13
Encyclopedia of the Middle Ages, Reference D 114 .E53 2000 v. 1-2
Encyclopedia of the Renaissance, Reference CB 361 .E53 1999 v. 1-6. V. 6 has article with bibliography on witchcraft. Also see witchcraft in the index.
Encyclopedia of European Social History from 1350 to 2000, Reference HN 373 .E63 2001. See the index. V. 3, pp. 361-371 has a chapter on witchcraft. Notice the arenas of life covered in each volume, marked on the spines.
Reader's Guide to Women's Studies, Main HQ 1180 .R43 1998. Although titled "Reader's Guide" is more of a one volume dictionary, albeit with several further reading references at the beginning of each entry. Topical and biographical entries. See witchcraft: ancient; witch hunts.
Schaus, Women and Gender in Medieval Europe, an Encyclopedia Main HQ 1147 .E85 W664 2006.
Wilson and Margolis, Women in the Middle Ages Main HQ 1143 .W643 2004 v. 1-2
Lawler, Encyclopedia of Women in the Middle Ages, Main HQ 1143 .L38 2001. Both topical and biographical entries, with further reading references.
Women's Studies Encyclopedia, Main HQ 1115 .W645 1989, v. 3. Some further reading references. See witchcraze
Medieval England, an Encyclopedia, Reference DA 129 .M43 1998. Topical and biographical entries. Both primary and secondary further reading references.
Historical Dictionary of Late Medieval England, 1272-1485, Main DA 175 .H56 2002. Biographical and topical articles with further reading references. Also has a subject index.
Tudor England, an Encyclopedia, Reference DA 315 .T753 2001. See witchcraft.
Historical Dictionary of Stuart England, 1603-1689, Main DA 375 .H57 1996. See witchcraft.
New Catholic Encyclopedia, Reference BX 841 .C25 2003 v. 1-14. Original edition of Catholic Encyclopedia, 1913, is available online also. 1913 and 1967 printed editions in Main. Roman Catholic Church's views on witchcraft; examine different editions to see how/if the Church's views have changed over the years.
Encyclopedia of Witchcraft and Demonology, Main BF 1503 .R6 1981. All historical witchcraft topics.
Encyclopedia of Witches and Witchcraft, Main BF 1566 .G85 1999. Mostly historical witchcraft topics.
Athlone History of Witchcraft and Magic in Europe, V. 3 covers the Middle Ages, Main BF 1569 .J63 2002. V. 4, covers the 18th and 19th centuries, Main, BF 1584 .E9 W58 1999. Main BF 1584 .E9 A55 2002 covers the period of the witch trials after the Middle Ages to the 18th c. Sometimes reading a secondary text is helpful; has bibliography.
Oxford Companion to United States History, Main E 174 .O94 2001. See Salem witchcraft.
American Heritage Encyclopedia of American History, Main E 174 .A535 1998. Use for witchcraft in America. See witchcraft.
Encyclopedia of Global Historical Writings, Main D 13 .G47 1998 v. 1-2. Useful if you wanted to study the work of a particular historian, schools of history, or historiography.