As one of the biggest religions, Islam has teachings concerning both faith and practice. The field of practice is generally divided into two parts: acts of worship (‘ibadat) and worldly transactions (mu‘amalat). Although change in the areas of faith and worship is definitely not accepted by Muslims, it is generally accepted that worldly affairs (mu‘amalat) can and have to change according to new circumstances. However, we need to ask some basic questions about this issue: What are the underlying principles of these changes? Exactly which areas are suitable for renewal? Who can decide on it. In this book, the author tries to answer these questions with special reference to a great scholar of the classical Islamic thought, al-Ghazali, and one of the prominent scholars of the modern Islamic thought, Muhammad Abduh.