Historically, the focus on measuring ROI of marketing communications funds has centred on commercial brands, but this has now expanded to include the non-profit sector, primarily as a requirement of funding agencies. Yet while there is no doubt that an understanding of the relative effectiveness of business actions can yield huge benefits and is an important tool when seeking to achieve competitive success, marketing professionals encounter unique challenges in their endeavour to measure the value of their work. This chapter examines both the benefits and the challenges faced by marketers. It discusses the relative value of the various methods used to analyse marketing effectiveness and ROI and concludes with some recommendations as to how to formulate a basic business case. This ensures that the message that is intended to be sent is what the target group is receiving.