Isabel Florence Hapgood was an American ecumenist, writer and translator, especially of Russian and French texts.

Hapgood was born in Boston, to Asa Hapgood and Lydia Anna Bronson Crossley, with her twin brother Asa. Their parents later had another son, William Frank Hapgood (who became a patent lawyer). Asa Hapgood was an inventor, and his family of English and Scottish descent had lived near Worcester, Massachusetts since the 17th century. Her mother's father had emigrated from England and owned a farm in Mason County, Kentucky. While Asa was sent to Harvard University, which did not accept women (and ultimately went into the paper business), Isabel attended Worcester's Collegiate Institute between 1863 and 1865, then transferred to Miss Porter's School in Farmington, Connecticut. She graduated in 1868, the year her father died. Hapgood showed considerable language abilities, mastering many Romance and Germanic as well as Slavic languages, including Russian, Polish and Church Slavonic.