Contents Historically, as urban areas developed, drainage systems were constructed to convey both foul and surface water away from properties. These systems discharged untreated effluent to receiving waters. However, in many locations the drainage systems were very poorly designed, resulting in flooding, which caused human health issues, including cholera. In Victorian times legislation for both water supply and sewerage services was introduced, giving powers to local authorities to provide potable water and sewage services to urban areas. This legislation has been updated over the years, resulting in major improvements to urban drainage systems. In addition to facilitating these improvements, the legislation has resulted in the responsibility for sewage services transferring from local authorities to private water companies. In this chapter, the different types of drainage system encountered are explained, together with the historical techniques used to design the urban drainage system. Over the past 20 years, the manner of and the tools used for design have evolved significantly, and some of the new methods being used are highlighted. These include hydraulic modelling techniques (which can be used to model both underground and above-ground drainage systems), integrated urban drainage and risk-based approaches to design.