The major national biographies can be excellent sources for biographies of major, in most cases dead, philosophers.

• United Kingdom: Dictionary of National Biography (Oxford University Press, 2004) Available online
• United States: American National Biography (Oxford University Press, 2000) Available online
• Belgium: Biographie nationale. (Brussells: Buggenhoudt 1866–1986) 44 v. West Campus Storage
• France: Dictionnaire de biographie française (Paris: Letouzey et Ané, 1933–2001) 19 vols. Olin Stacks CT143 D5
• Germany: www.deutsche-biographie.de An online version of both the Allgemeine deutsche Biographie [ADB] (Berlin: Duncker & Humboldt, 1875–1912) 56 vols. and Neue deutsche Biographie  [NDB] (Berlin: Duncker & Humboldt, 1953–)
• Italy: Dizionario biografico degli Italiani (Rome: Istituto della Enciclopedia italiana, 1960–) 44 cols. (to M) Olin Stacks DG463 .D5 
• Netherlands: Nieuw Nederlandsch biografisch woordenboek (Leiden: Sijthoff, 1911–1937) 10 vols. Olin Stacks CT1143 .M

See also the Biography and genealogy master index (Gale).

To find more in-depth information about a particular area of philosophy, there are a number of more specialized reference works that are worth consulting. Many of these available in the following series:

• Oxford Handbooks Online - Philosophy

• Blackwell Companions to Philosophy

• Blackwell Philosophy Guides

• Historical dictionaries of religions, philosophies, and movements (Scarecrow Press)

• Philosophy A to Z (Edinburgh University Press)

The following titles are useful sources of in-depth information on particular subfields of philosophy

Aesthetics

• Encyclopedia of aesthetics / Michael Kelly, editor-in-chief (Oxford University Press, 1998) 4 vols. Olin Reference, Art Reference BH56 .E53 1998 Available Online
• Oxford Art Online A database of art terminology, encyclopedic entries on artists and works of art, and images.
• The Oxford handbook of aesthetics / edited by Jerrold Levinson. (Oxford University Press, 2003) Olin Stacks
  BH56 .O94 2003
  

Ancient Philosophy

• Encyclopedia of classical philosophy / edited by Donald J. Zeyl (Greenwood Press, 1997) Olin Reference B163 E53
• Greek thought : a guide to classical knowledge / edited by Jacques Brunschwig and Geoffrey E.R. Lloyd (Harvard University Press, 2000) Olin Stacks DF78 .S2213 2000
• Oxford Classical Dictionary / edited by Simon Hornblower and Anthony Spawforth. 3rd edition. (Oxford University Press, 2003.) Olin Reference DE5 .O9 2003 Online Access
• Thesaurus Linguae Graecae. Online digital library of Greek literature from Homer to the Fall of the Byzantine Empire.

"Continental Philosophy"

• Dictionary of continental philosophy / edited by John Protevi (Yale University Press, 2006) Olin Reference B41 D46
• The Columbia history of twentieth-century French thought / edited by Lawrence D. Kritzman (Columbia University Press, 2006) Olin Stacks DC33.7 .C575 2006
• The Oxford handbook of continental philosophy / edited by Brian Leiter and Michael Rosen (Oxford University Press, 2007) Olin Stacks B803 .O94 2007

Ethics

• Encyclopedia of applied ethics / Ruth Chadwick, editor-in-chief. (Academic Press, 1998) 4 vols. Olin Reference BJ63 E44 1998
• Encyclopedia of bioethics / edited by Stephen G. Post. 3rd edition. (MacMillan Reference, 2004). 5 vols. Olin Reference BJ63 E44 1998
• Encyclopedia of ethics / Lawrence C. Becker and Charlotte B. Becker, editors. 2nd edition. (Routledge, 2001) 3 vols. Olin Reference
• Oxford handbook of practical ethics / edited by Hugh LaFollette. (Oxford University Press, 2003) BJ1031 .O94 2003

Metaphysics & Epistemology

• Handbook of metaphysics and ontology / editors, Hans Burkhardt, Barry Smith (Philosophia Verlag, 1991) Olin Stacks BD111 H225 1991
• The Oxford handbook of epistemology / edited by Paul K. Moser. (Oxford University Press, 2002) Olin Stacks BD161 .O96 2002
• The Oxford handbook of metaphysics / edited by Michael J. Loux and Dean W. Zimmerman. (Oxford University Press, 2003) Olin Stacks BD111 .O94 2003

Philosophy of Language & Logic

• Concise Encyclopedia of philosophy of language / edited by Peter V. Lamargue (Pergamon, 1997) Olin Stacks P106 C5946 1997
• Dictionary of logical terms and symbols / Carol Horn Greenstein (Van Nostrand Reinhold, 1978) Olin Stacks QA9 G698
• Dictionary of philosophical logic / Roy T. Cook (Edinburg University Press, 2009) Olin Reference BC 9 C66 2009
• Handbook of logic and language / edited by Johan van Benthem & Alice ter Meulen (Elsevier/MIT Press, 1997) Olin Stacks QA76.9 N38 H36 1997
• Key thinkers in linguistics and the philosophy of language / edited by Siobhan Chapman and Christopher Routledge. (Oxford University Press, 2005) Olin Stacks P107 .K49 2005
  
• Logic from A to Z / Michael Detlefsen, David Charles McCarty & John B. Bacon (Routledge, 1999) Olin Stacks QA9 .D47 1999

Philosophy of Mind

• Dictionary of cognitive science / Olivier Houdé, editor (Psychology Press, 2004) Olin Reference BF311 .V56713 2004
• Dictionary of the Philosophy of Mind / edited by Chris Eliasmith online.
• Encyclopedia of cognitive science / Lynn Nadel, editor in chief. (Nature Publishing Group, 2003) 4 vols. Olin Reference BF311 .E53 2003
• MIT encyclopedia of the cognitive sciences / Robert A. Wilson & Frank C. Keil, editors. (MIT Press, 1999) Olin Reference BF311 .M556 1999 A
• Oxford companion to consciousness / edited by Tim Bayne, Axel Cleeremans, Patrick Wilken (Oxford 2009) Olin Stacks. Available online.
• The Oxford companion to the mind / edited by Richard L. Gregory. 2nd edition (Oxford University Press, 2004) Olin Reference BF31 .O94 2004 Available online
• The Oxford handbook of philosophy and neuroscience / edited by John Bickle. (Oxford University Press, 2009) Olin Stacks
• The Oxford handbook of philosophy of mind / edited by Brian P. McLaughlin with Ansgar Beckermann and Sven Walter. (Oxford University Press, 2009) Olin Stacks BD418.3 .O94 2009

Political Philosophy

• The Blackwell dictionary of twentieth-century social thought / edited by William Outhwaite & Tom Bottomore (Blackwell, 1993) Olin Stacks H41 B53 1993
• The philosophy of law : an encyclopedia / editor, Christopher Berry Gray (Garland, 1999) 2 vols. Law Library K204 .P49 1999
• The Routledge dictionary of twentieth century political thinkers / edited by Robert Benewick & Philip Green. 2nd edition. (Routledge, 1997) Olin JA83 R725 1997