A circular letter is a written document that is addressed for circulation to a group of people. It is usually formal and official. It may be for a closed group or general distribution. The term may refer to:

• Flyer (pamphlet), a single page leaflet
• Circular Letter (Interlingua), an early Interlingua publication
• Circular letter or encyclical, a letter written by a bishop and addressed to his clergy
• Massachusetts Circular Letter, a statement written by Samuel Adams

• Gillian Harrison
• Gillian Hicks
• Gillian Hodges
• Gillian Hopwood
• Gillian Howell
• Gillian Jagger
• Gillian Jerome
• Gillian Johnston (murder victim)
• Gillian Joynson-Hicks
• Gillian Joynson-Hicks, Viscountess Brentford
• Gillian Keegan
• Gillian Kennedy
• Gillian K. Ferguson
• Gillian, Lady Greenwood of Rossendale
• Gillian Laub
• Gillian Leng
• Gillian Lester
• Gillian Lovegrove
• Gillian Maclaine
• Gillian Margaret Howell
• Gillian Margaret Moore
• Gillian Martin
• Gillian Matthewson
• Gillian McAllister
• Gillian McCall