Among the topics covered in this introduction to the largest and oldest institution in the world are the origins of the Catholic Church, how Catholicism has changed and adapted over the centuries and the challenges the Catholic Church faces in the 21st century. What are the origins of the Catholic Church? How has Catholicism changed and adapted over the centuries? What challenges does the Catholic Church face in the twenty-first century? Gerald O'Collins answers these and other questions in this clear, accessible introduction to the largest and oldest institution in the world. Despite a long history of external threats and internal strife, the Roman Catholic Church and the broader reality of Catholicism remain a vast and valuable presence into the third millennium of world history.