ARTICLE Laurila_PMC_2013/IDIAP From Big Smartphone Data to Worldwide Research: The Mobile Data Challenge Laurila, J. K. Gatica-Perez, Daniel Blom, Jan Bornet, Olivier Do, Trinh-Minh-Tri Dousse, O. Eberle, Julien Miettinen, Markus EXTERNAL PUBLIC Pervasive and Mobile Computing 9 6 752–771 2013 This paper presents an overview of the Mobile Data Challenge (MDC), a large-scale research initiative aimed at generating innovations around smartphone-based research, as well as community-based evaluation of mobile data analysis methodologies. First, we review the Lausanne Data Collection Campaign (LDCC) -- an initiative to collect unique, longitudinal smartphone data set for the MDC. Then, we introduce the Open and Dedicated Tracks of the MDC; describe the specific data sets used in each of them; discuss the key design and implementation aspects introduced in order to generate privacy-preserving and scientifically relevant mobile data resources for wider use by the research community; and summarize the main research trends found among the 100+ challenge submissions. We finalize by discussing the main lessons learned from the participation of several hundred researchers worldwide in the MDC Tracks.