The purpose of this report is to re-examine the scientific and grey literature on current methods of estimating the size of illegal markets, with an emphasis on the meth/MDMA markets. The first part of this paper reviews the current data available from various surveys on the prevalence of Amphetamine-Type Stimulants (ATS) and MDMA use in Canada. The second section of the report examines recent innovations in the area, with a special emphasis on two families of methods: (i) multiplier methods, which derive an estimate of the population based on a rate of occurrence of an event in the population of interest (e.g. number of overdoses per ATS user); and (ii) capture-recapture methods, which infer the number of users, dealers or producers never arrested based on the patterns of arrests and re-arrests over a fixed time period. The third part of the paper turns to the data requirements for applying these methods to the Canadian meth and ecstasy markets, with an emphasis on estimating the scale of ATS production.