Harriet Teresa Law (née Frost, 5 November 1831 – 19 July 1897) was a leading British freethinker in 19th-century London. The daughter of a small farmer, she was raised as a "Strict Baptist" but later converted to atheism. She became a salaried speaker for the secularist movement and addressed many often hostile audiences around the country. She was invited to sit on the general council of the First International, the only woman to do so, where she engaged in debate with prominent communists including Karl Marx and Friedrich Engels. From 1877 to 1878 she published The Secular Chronicle, which covered subjects such as socialism, atheism and women's rights.