This article describes the challenges posed by optical musicrecognition – a topic in computer science that aims to convert scannedpages of music into an on-line format. First, the problem is described;then a generalised framework for software is presented that emphasises keystages that must be solved: staff line identification, musical objectlocation, musical feature classification, and musical semantics. Next,significant research projects in the area are reviewed, showing how eachfits the generalised framework. The article concludes by discussingperhaps the most open question in the field: how to compare the accuracy and success of rival systems, highlighting certain steps thathelp ease the task.