In this article, the first of two, the recent developments and current situation in the private rented sector are examined. Four roles for the sector are identified: housing those who traditionally lived in the sector, housing the young and mobile, providing accommodation with employment and acting as a tenure of last resort for those unable to find accommodation in the majority tenures. The types of household to be found in each sub-sector are described and their reasons for being in the sector and what they obtain are analysed. Different types of landlord are identified and their reasons for letting examined. The problems encountered by tenants and landlords in each sub-sector are described, leading to the conclusion that the private rented sector urgently requires considered and effective attention from policy makers.