Recently, smartphones had big success and the download-numbers as well as the number of App's themselves nearly seem to explode. This thesis provides an insight about the Android-System itself, related studies and actual developments in the field of smartphone-usage. Therefore, a universal experience-sampling questionnaire tool Fragebogen is extended with required functional- ity. It should help researchers to gather suitable information about situations and circumstances affecting App-usage. Additionally, the tool enables developers to gather reliable feedback about strengths, weaknesses and possible suggestions of improvement about their Apps. First application for Fragebogen takes place in a 14-day field test, examining usage of the official Wikipedia-App. This serves as a natural test environment for Fragebogen and generates a data set that is analyzed in order to compare it's results to the actual state of knowledge.