Introduction

Abstract

Sound decision making requires the optimal use of available data on the topic at hand. Whenever evidence is multifaceted, abundant, or otherwise complex to face, specifi c tools must be envisioned for informed decision making. Historically, reviews were the fi rst type of evidence synthesis tool. Subsequently, meta-analyses have complemented the most refi ned type of reviews (i.e. systematic reviews). This fi eld of research methodology has been further expanded by the recent availability of umbrella reviews, overviews of reviews and meta-epidemiologic studies, which provide a more general framework for evidence synthesis and decision making, encompassing multiple sources of information (e.g. different systematic reviews on the same topic, or different systematic reviews on different but connected topics). This chapter serves as the introduction to our textbook devoted to this novel and fascinating topic.