This introduction presents an overview of key concepts discussed in this book. The book reviews the basic architecture of electronic health records (EHRs), focusing on the database as the underlying entity, and then moves into challenges in accessing the data including data extraction and linkage issues. This is a crucial step in the research continuum, and unfortunately is only viewed as a "black box", that is, a request for data is made and data are provided that may or may not be correct. This results in a dataset missing data on some key factors while containing information extraneous to the question at hand. The book presents the core epidemiology, introducing essential study designs and statistical techniques needed to analyze "secondary" data, in other words, data retrieved from the EHR. It concludes with a discussion of population health and moving from knowledge generation to knowledge dissemination through translational epidemiology.