OpenStreetMap (OSM) is the biggest and best-known source for open geographic information gathered by crowds of volunteer enthusiasts worldwide. With the needs for open-source geodata increasing, OSM has taken steps to increase its visibility towards potential users as well as usability of its tools for new contributors. As the ease of using OSM editors is vital to attracting a greater amount of contributing members, usability evaluations of the tools are needed in order to provide a solid and growing basis of volunteers for the project. The iD editor for OSM is one of the most recently developed tools and, being the default online editor for OSM, it is also the most used. The objective of this study is to investigate the usability of the iD editor. To this end usability tests have been conducted with users selected with the aid of an online survey. The participants were given mapping tasks to complete using iD and observed with the thinking aloud method as well as screen recording and mouse/keyboard logging. Additionally the test persons were interviewed after each test. The data gathered were analysed with regard to key usability criteria such as learnability, efficiency, error tolerance, and subjective user satisfaction. The outcome of this study is the identification of usability issues from which possible improvements of the tool have been derived. The study shows that iD is an overall usable tool for novice users, but still shows opportunities for improvement especially in terms of learnability and error handling.