The importance of search as a medium for travel advertising and promotion has grown dramatically over the past ten years. According to industry researcher PhoCusWright, when consumers are comparing and choosing travel services, they use search engine websites more than travel suppliers. Forrester reports that consumers use these sites slightly less than they do online travel agencies. Search engine marketing spending is expected to represent nearly $1 of every $10 spent on both online and traditional marketing within three years. This report describes some of the tools available to measure return on investment (ROI) and some key performance indicators (KPIs) associated with search engine marketing. It provides two simple analyses that rely on freely available tools for measuring search marketing performance. It also presents the challenges of interpreting results from these and other tools and processes used to measure search engine marketing effectiveness.