Tremor is the most common movement disorder. However; characterizing it in large populations is not easily accomplished since current methodologies are not adapted to large-scale field studies. To overcome this challenge, a smartphone application was developed as a stand-alone platform to assess tremor. The current book chapter details the steps taken to validate this mobile application. Data recorded with the smartphone was analyzed online and offline as well as compared to laboratory equipment and a clinical scale. This allowed for the identification of the tremor properties that could reliably be characterized with the smartphone as well as the limits of the hardware. It also allowed for the identification of tasks that could be performed with the smartphone when tremor was being assessed. Finally, we confirmed the clinical relevance of the results provided by the smartphone application.