Summer Fields is a fee-paying boys' independent day and boarding preparatory school in Summertown, Oxford. It was originally called Summerfield and used to have a subsidiary school, Summerfields, St Leonards-on-Sea (known as "Summers mi[nor]").

Summerfield became a boys' preparatory school in 1864, with seven pupils. Its owner, Archibald MacLaren, had been educated at Dollar Academy and was a fencing teacher who ran a gymnasium in Oxford. He believed strongly in the importance of physical fitness. His wife, Gertrude, was a classical scholar and teacher, a daughter of David Alphonso Talboys. The school motto is Mens sana in corpore sano, "A healthy mind in a healthy body".

The school grew and needed more staff, two of whom married into the Maclaren family: the Reverend Dr Charles Williams ("Doctor"), who took over the scholarship form from Mrs Maclaren and married Mabel Maclaren in 1879, and the Reverend Hugh Alington, who married Margaret Maclaren in 1885 and took over the boys' games. The school remained in the hands of the Maclaren, Williams, and Alington families for its first 75 years.

At the end of the 19th century, "Doctor" became headmaster and there was much building at the school. A second school, "Summers mi", was opened at St Leonards-on-Sea, Sussex, for boys to benefit from the sea air. In 1918 Doctor passed the headmastership on to Hugh Alington. There was a lean spell in the 1930s, and numbers fell, but John Evans and Geoffrey Bolton ("G.B.") took over in 1939. During the Second World War three other schools were evacuated to Summer Fields – Famborough School, Hampshire, Summers mi, and St Cyprian's School from Eastbourne – and this restored the numbers.

In 1955, the school became a charitable trust, with a board of governors, including Harold Macmillan, who had been at the school as a boy and was soon to become prime minister.

During the 1960s, Pat Savage was headmaster, with the assistance of Jimmy Bell and Pat Marston. By the centenary year in 1964, the school's appearance had changed relatively little (see illustration), but it was thriving and energetic enough to celebrate with a hardback book of 332 pages, with contributions from "O.S.", or Old Summerfieldians, including stories about Archibald Wavell, 1st Earl Wavell, and Harold Macmillan, and a friendly greeting in verse from the arch-rival Horris Hill School. A former pupil recollected Pat Marston as follows:

Then I met the Ogre. For my first few weeks I was terrified by this "monster". His appearance was formidable. He growled and shook the room as he entered. But once I learnt that he didn't actually eat little boys, even on Black Fridays, the classes became amusing, exhilarating and even relaxing.

In 1975, Nigel Talbot Rice took over as headmaster. He put the school on a sound financial footing through a series of appeals which paid for an ambitious building programme: new classrooms, the Macmillan Hall and Music Centre, an indoor swimming-pool, the Wavell Arts and Technology Centre (named after Earl Wavell), and the Sports Hall. In 1997, Talbot Rice retired and was succeeded by Robin Badham-Thornhill. In 2010 David Faber, an old boy and governor, took over as headmaster.