Thomas Phaer (also spelled Phaire, Fayre, Faer, Phayre, Phayer) (c. 1510 – 12 August 1560) was an English lawyer, pediatrician, and author. He is best known as the author of The Boke of Chyldren, published in 1545, which was the first book on pediatrics written in the English language.
It is thought that Phaer was born in Norwich. His father, also Thomas, was of Flemish descent. Phaer was educated at Oxford University. He studied law at Lincoln's Inn, and became Solicitor in the Court of the Welsh Marches; on his appointment he settled at the Welsh town of Cilgerran near Cardigan, where he lived until he died.
He was Member of Parliament for Carmarthen Boroughs in 1547 and for Cardigan for (1555–1559).
He applied to Oxford University for the degree of Bachelor of Medicine in February 1558, stating that he practised for twenty years. He was granted his Bachelor's, and then a Doctorate of Medicine, later that year.
Phaer died in Cilgerran, leaving his wife, Ann, and three daughters, Eleanor, Mary, and Elizabeth. He was buried in the local parish church. He is commemorated as one of the supporters in the coat of arms of the Royal College of Paediatrics and Child Health. The other supporter is June Lloyd.