In two series: v1-15 offers alphabetical coverage of the ancient world while the second series, v.1-4, offers articles on the legacy and reception of classical ideas and culture.
The ultimate scholarly treatment, an update to Pauly-Wissowa.

Detailed, scholarly guides on topics such as the Hellenistic World, Roman Warfare, art and architecture, or specific authors or literary genres.

Offers signed articles on people, places, events, and ideas of the ancient Mediterranean, including the Near East and Egypt in addition to the Greek and Roman worlds

3v Long chapters by leading scholars on topics such as geography, family life, economics, etc.

Short articles with an emphasis on material culture and social history,

Short articles with an emphasis on material culture and social history.

A scholarly treatment of the period from 250 to 800 C.E., with several introductory chapters on topics such as “Barbarians,” “Islam,” and “Religious Communities.”

34+ 15v. + suppl. index.
Usually cited as Pauly‐Wissowa or PW, the standard, scholarly German work covering the entire body of classical literature, history, antiquities, biography, and other fields. The arrangement is somewhat complicated, as there are 15 supplementary volumes with additions and corrections. Use the index to locate new and revised material in the supplementary volumes. Now modernized as Brill's New Pauly.

Some volumes are freely available online in Hathitrust or at German Wikipedia which offers detailed indexes online

Provides summary chapters that outline the issues, history of inquiry, basic sources, and methodologies for each field within classical studies.

Offers an annotated bibliography of book-length reference works, covering the rise and fall of the Greek and Roman civilizations from the Bronze Age through the 6th century AD.

Lists and describes resources for all fields of Classics; includes journal articles and monographs as well as reference books.

The Cambridge Greek Lexicon is based upon principles differing from those of existing Greek lexica. Entries are organised according to meaning, with a view to showing the developing senses of words and the relationships between those senses.

A comprehensive dictionary of ancient Greek, based on historical principles. There are also abridged versions for students.

Specialized vocabulary and word forms found in the Homeric epics; frequently revised. Includes lists of place and personal names.

Anauthoritative dictionary of classical Latin, with comprehensive coverage of the language from its beginnings until AD 200.

One of the classic works of lexicography; familiarly known as "Lewis and Short."