This document complements previous technical guidance documents on planning and executing illegal, unreported and unregulated (IUU) fishing estimation studies by providing a catalogue of 26 estimation methodologies from published studies. These methodologies encompass a wide range of locations, fishing gear and IUU fishing types. The catalogue is organized around two ways of identifying relevant methodologies: a) the IUU fishing estimation approach; and b) the primary available data source. The five types of IUU fishing estimation approaches (“a”) include: 1) estimating total catch minus reported catch; 2) partitioning total catch into IUU/non-IUU fishing; 3) summing individual IUU fishing events to a total amount; 4) estimating “true” catches for suspect vessels or fleets; and 5) determining relative amounts or trends in IUU fishing. The four types of primary data sources (“b”) include: 1) fishery models; 2) commercial sources; 3) operational data; and 4) expert judgements, comparisons to catch compilations and stakeholder surveys. These two types of approaches help to identify the relevant methodologies presented as concise, individual one- to two-page summaries. Each methodology is described in terms of the key elements needed and how they can be sourced, the specific steps involved in constructing the estimate, and guidance on the applicability of the method.