Lotte World Tower (Korean: 롯데월드타워), is a 123-story, 555 m (1,821 ft) supertall skyscraper, located in Sincheon-dong, Songpa-gu, Seoul, South Korea. It is the sixth-tallest building in the world, the tallest in OECD countries, and also the first in South Korea to be over 100 stories tall.

It was the fourth-tallest in the world when completed in 2016, though it was surpassed by the 599 m (1,965 ft) supertall Ping An Finance Center in Shenzhen, China, which was completed on March 28, 2017, and the 678.9 m (2,227 ft) supertall Merdeka 118 in Kuala Lumpur, Malaysia, which was topped out on November 30, 2021. The tower opened to the public on April 3. Haeundae LCT The Sharp in Busan is the second-tallest building in the country.

On March 17, 2016, before the final phase of external construction, the Diagrid lantern-shaped roof structure was completed. The roof structure was constructed with steel counterparts that are each 12 m (39 ft) and weigh 20 tons. The counterparts were made up of bent metal panels that are 6 cm (2.4 in) thick. The roof structure itself is 120 m (390 ft) high and covers floors 107–123. Approximately 3,000 tons of steel parts, a high-precision 64t tower crane and GPS alignment systems, as well as welding technicians, were used in the construction of the roof.

The roof structure is engineered to withstand its weight without reinforcing pillars, endure earthquakes up to a magnitude of 9 under the Richter magnitude scale, and winds up to 80 m/s (260 ft/s).

The exterior of pale-coloured glass draws inspiration from Korean ceramics and features accents of metal filigree