The Heidelberg Catechism was first issued in the kingdom of the Electoral Palatinate in the year 1563. As early as 1623 it was translated into the Malay language, a predecessor of the modern-day Indonesian language. This Malay translation was used all over the Indonesian archipelago to teach newly converted Christians and to prepare them for baptism. Even now the Heidelberg Catechism is used in many Indonesian churches and connects them to many other reformed churches all over the world where the Heidelberg Catechism is being used also. One of these Indonesian churches is the Christian Church from North-Central Java (Gereja Kristen Jawa Tengah Utara - GKJTU), a fruit of the missionary work of Neukirchen Mission and Salatiga Mission. Nevertheless, in the 21st century the Indonesian churches have to face many new challenges in the field of culture, religious plurality, science and technology, etc. As an answer to these challenges the Synod Assembly of the Christian Church from North-Central Java launched this 21st Century Update of the Heidelberg Catechism in 2008. Even for Christians outside Indonesia these 69 questions and answers may be helpful in facing modern challenges which are surprisingly similar in Indonesia and in other parts of the world, such as: "How can culture be renewed?" - "According to the Christian faith, where does religious plurality come from?" - "May the church be active in politics?" - "Does salvation in Christ also affect science, humanities and technology?" - and 65 other interesting questions and answers, all of them very brief, concise and biblically based. The purpose of this annotated English translation is to make these questions and answers accessible for Christians outside Indonesia.