This paper reviews the meaning and measurement of unobserved economies germane to tax evasion and macroeconomic information systems. These include the unreported, non-observed, underground, illegal, informal and unrecorded economies. It reviews the progress and shortcomings of national and international agency efforts to measure these unobserved economies, noting what they have in common, what distinguishes one from another and their interconnections. It then examines the meaning of Professor Schneider's Shadow Economy (SSE), and the veracity of his claim to have accurately estimated its size and trend worldwide by employing a MIMIC model methodology. It concludes that SSE estimates suffer from conceptual flaws, apparent manipulation of results and insufficient documentation for replication, questioning their place in the academic, policy and popular literature.JEL classification: E26, O17, H26, E41, C51, C82, K42.