Essex Street Chapel, also known as Essex Church, is a Unitarian place of worship in London. It was the first church in England set up with this doctrine, and was established when Dissenters still faced legal threat. As the birthplace of British Unitarianism, Essex Street has particularly been associated with social reformers and theologians. The congregation moved west in the 19th century, allowing the building to be turned into the headquarters for the British and Foreign Unitarian Association and the Sunday School Association. These evolved into the General Assembly of Unitarian and Free Christian Churches, the umbrella organisation for British Unitarianism, which is still based on the same site, in an office building called Essex Hall. This article deals with the buildings, the history, and the current church, based in Kensington.

Unitarianism is a nontrinitarian branch of Christianity. Unitarian Christians affirm the unitary nature of God as the singular and unique creator of the universe, believe that Jesus Christ was inspired by God in his moral teachings and that he is the savior of humankind, but he is not equal to God himself.