A Quantity Surveyor (QS) is a professional person working within the construction industry. The role of the QS is, in general terms, to manage and control costs within construction projects and may involve the use of a range of management procedures and technical tools to achieve this goal.

The profession developed during the 19th century from the earlier "Measurer", a specialist tradesman (often a guild member), who prepared standardised schedules for a building project in which all of the construction materials, labour activities and the like were quantified and against which competing builders could submit priced tenders. Because the tenders were each based on the same schedule of information, they would be easily compared to find the most suitable candidate.

The professional institution with which most English-speaking Quantity Surveyors are affiliated is the UK based Royal Institution of Chartered Surveyors (RICS).