The world's largest telescope is the Extremely Large Telescope (ELT), currently under construction in Chile. It's a reflecting telescope.

Here's why:

* Reflecting telescopes use mirrors to gather and focus light. This design allows for larger primary mirrors (the main mirror that collects light) to be built more easily and economically compared to refracting telescopes.

* Refracting telescopes use lenses to focus light. Larger lenses are incredibly heavy, difficult to manufacture, and prone to distortions, making them less practical for large telescopes.

The ELT will have a primary mirror with a diameter of 39.3 meters, making it by far the largest optical/near-infrared telescope in the world.