Sir William Reynell Anson, 3rd Baronet, PC, FBA (14 November 1843 – 4 June 1914) was a British jurist and Liberal Unionist turned Conservative politician from the Anson family.

Anson was born at Walberton, Sussex, the eldest son of Sir John William Hamilton Anson, 2nd Baronet, and his wife Elizabeth Catherine (née Pack).

Educated at Eton, 1857–62,[1] and Balliol College, Oxford, 1862–66, he took a first class in both Classical Moderations, 1863, and Literae Humaniores ('Greats', a combination of philosophy and ancient history), 1866.

In that year he was returned, without opposition, as Member of Parliament (MP) for Oxford University in the Liberal Unionist interest, and consequently resigned the vice-chancellorship.

1906), and on The Law and Custom of the Constitution in two parts, "The Parliament" and "The Crown" (1886–1892, 3rd ed.