Thomas Day (22 June 1748 – 28 September 1789) was a British author and abolitionist. He was well known for the book The History of Sandford and Merton (1783–1789) which emphasized Rousseauvian educational ideals, for his writings against slavery, for campaigning both for and against American independence, and for his project applying his educational ideals to young girls with the aim of raising a wife for himself.