APA (7th ed.) Citation

(1990). The new encyclopaedia Britannica (15th ed., reimp.). Encyclopaedia Britannica.

Chicago Style (17th ed.) Citation

The New Encyclopaedia Britannica. 15th ed., reimp. Chicago [etc.]: Encyclopaedia Britannica, 1990.

MLA (9th ed.) Citation

The New Encyclopaedia Britannica. 15th ed., reimp. Encyclopaedia Britannica, 1990.

Warning: These citations may not always be 100% accurate.