This study series “Shia Islam” - as part of Shiite thought and faith - shows a rational trait and is imbued by the spiritual spirit. It is also based on the idea of the unity of knowledge that fills it, and accordingly it does not allow contradictions to apply among the Islamic systems, but considers in them only different forms of expression of one and the same truth. It presents the Shiite moral, spiritual and rational teachings in the form of core treatises - and gives them a concise expression. After decades of living in Europe, I noticed that people today are increasingly looking for authentic sources about Shia Islam. For various reasons, people are interested in Shia Islam and would like to learn more about it. But when they search for the authentic sources or ask about the real topics about “Shia Islam”, they find that there are only a few books about it - especially in the German-speaking world. Therefore, in 21st century it is an urgent necessity to present Shia Islam and especially its spirituality through studies and books. This study has been carried out to fulfill this need.