Polymer Foams are used in many different types of applications and it is hard to find an area where they are not utilised. Polyolefin Foams are a relatively recent development compared to the other types of foam. The Polyolefin foam processes were developed in the 1960s and 1970s. This Review starts with a brief history of the subject and then reports on the current situation regarding Polyolefin Foams. The section on processing discusses the properties required for successful foam production. The polymer section then describes the molecular structures necessary to produce the required properties and then considers novel polymer that can be used for foams. The properties section covers the mechanical and thermal properties and how these can be used to best advantage, while the applications section discusses how these properties can be used.