In collaboration with our colleagues from Nordic Alcohol and Drugs Studies, Drugs and Alcohol Today has planned this ebook on poly-substance use. We recognise a need to return to this topic in order to explore some of the combinations of drugs and substances which are emerging in the age of on-line markets and purchasing and novel psychoactive substances. We also wanted to high-light some of the combinations which receive less mainstream and political attention. The traditional or conventional combination which receives most attention and publicity seems to be crack cocaine and heroin, airily referred to as 'Class A drugs' by many of our politicians and commentators. This ease of use may persuade many that such voices know what they are talking about; and in so-doing narrow the understanding amongst the wider public of the complexity of drug issues, use and responses. This reductionist understanding is sometimes grudgingly extended to include alcohol. While retaining an awareness of the role of alcohol, this ebook includes papers which look at less acknowledged combinations, and one combination with the potential to reduce 'Class A' drug use by making use of a Class B drug. What we are publishing in this ebook has a wide geographical range, a reflection of the growing interest, in readership and authorship, that DAT is attracting. The papers in this ebook also reflect an extended coverage of both substances and situations where poly-substance use takes place.