The 1998 Rome Statute, the treaty establishing the International Criminal Court (ICC), includes a longer list of gender-based crimes than any previous instrument of international criminal law. The Statute's twentieth anniversary provides an opportunity to examine how successful the ICC has been in prosecuting those crimes, what challenges it has faced, and how its caselaw on these crimes might develop in future. Taking up that opportunity, this book analyses the ICC's practice in prosecuting gender-based crimes across all cases for war crimes, crimes against humanity and genocide in the ICC up until mid-2018. This analysis is based on a detailed examination of court records and original interviews with prosecutors and gender experts at the Court. This book covers topics of emerging interest to practitioners in this field, including wartime sexual violence against men and boys, persecution on the grounds of gender and sexual orientation, and sexual violence against 'child soldiers'.