The correct answer is **Christianity**.

**Key Points for Study and Exams:**
- Christianity is the **largest religion in the world**, with over **2.3 billion followers** (around 31% of the global population).
- It is followed closely by **Islam**, which has over **1.9 billion followers**.
- The religion is based on the teachings of **Jesus Christ** and has major denominations like Catholicism, Protestantism, and Eastern Orthodoxy.
- This is a frequently asked question in **competitive exams, entrance tests, and GK quizzes** related to demographics and world culture.

**Remember:** Christianity is the most followed religion globally.