The Cass Business School (officially Sir John Cass Business School, City of London) is a very highly-ranked, world-class business school located in the City of London, England, and is part of The City University, London. It was formerly called the City University Business School. It is accredited by AMBA and EQUIS and offers Specialist Master's Programmes, MBA (Master of Business Administration) and Executive Programmes. The School is housed in a building located in the City of London, which caters predominantly for postgraduates. It also offers a range of undergraduate courses. The School offers an EMBA China programme in China which is aimed at Chinese students.

Cass was ranked 4th in the international league table of top business schools published by the Social Science Research Network in May 2006. It has also ranked very highly in previous years: the Financial Times Executive MBA Rankings 2005 ranked it as 10th in the world, 2nd in the UK and 3rd in Europe; Cass gained 2nd place overall in UK and 6th in Europe in the Financial Times Survey of European Business Schools 2004. The School has almost 13,000 alumni globally.

Cass recently announced plans for a second campus at Canary Wharf, catering mainly for its Executive Education wing CassExec. The campus will be housed in One Canada Square.

The Cass Business School is divided into three faculties. These faculties are the Faculty of Actuarial Science, Faculty of Finance and the Faculty of Management.