The LMA Exposure Management Working Group (EMWG) was formed to look after the interests of catastrophe ("cat") modellers working in the Lloyd's market. Given the increasing use of cat models in the market in recent years and their perceived complexity and sophistication, the EMWG agreed that it would be useful to put together a simple guide for colleagues not working on cat modelling. The aim of this guide is therefore to provide some of the background information as to what a cat model is, explain the terminology frequently used by modellers, and answer many of the most frequently asked questions on cat models. This document is not intended to be a comprehensive guide to cat modelling or to answer all questions on this subject. It will hopefully provide non-cat modellers with a basic understanding of the work of cat modellers, and also act as a quick reference document on cat models.