This research paper, commissioned by Propertymark, examines the impact of Section 24 of the Finance (No2) Act 2015 on buy-to-let landlords in England. This legislation, introduced in 2015 and phased in over four years, gradually reduced the amount of tax relief landlords could claim on mortgage interest payments, from 100% to the basic rate of 20%. The report aims to understand how this change has affected landlords' financial situations, their investment decisions, and the broader private rented sector (PRS) in England.