Lady Charlotte Guest, nee Bertie (May 19, 1812 - January 15, 1895), was an important figure in the history of the study of Welsh literature and language. She is best known for her pioneering translation of the major medieval work, the Mabinogion.

She was daughter of the Earl of Abingdon by his second wife (who went on to remarry a clergyman, and have another daughter who married the Marquis of Huntly ). She was unhappy living with her mother and stepfather, and, after what may have been a a brief flirtation with the future Prime Minister Benjamin Disraeli, escaped through marriage, which was however, not a conventional one for her age. Her husband, John Josiah Guest, was an industrialist in Wales, the owner of the Dowlais ironworks and rather older than her; they moved to Merthyr Tydfil after he was elected MP for the constituency in 1832. Lady Charlotte was very happy in her marriage, and took an enthusiastic interest in her husband's philanthropic activities on behalf of the local community. Guest eventually obtained a baronetcy in 1838. During her time in Wales, Lady Charlotte learned Welsh and translated (and censored) several medieval Welsh songs and poems and eventually the Mabinogion, also in 1838. Following the death of her first husband, she married Charles Schreiber , a Member of Parliament, and left Wales permanently. Other interests took over her life, including a collection of ceramics which she bequeathed to the Victoria and Albert Museum.

Lady Charlotte's eldest son Sir Ivor Guest, 2nd Bt, eventually became First Baron Wimborne and married Lady Cornelia Spencer-Churchill, eldest daughter of the Seventh Duke of Marlborough and thus aunt to Winston Churchill. They were parents of the First Viscount Wimborne. Among her other descendants are the American Guests (the late socialite C. Z. Guest was wife of one of these), the Earls of Bessborough, the Viscounts Chelmsford, and others.

Lady Charlotte Guest was a "foreigner" (non-Welsh person) who helped revive Welsh culture. She is remembered, along with her near-contemporary Lady Llanover, as a great patron of the arts in Wales.