The Siam Cement Public Company Limited or SCG is the largest cement company in Thailand. It is listed on the Stock Exchange of Thailand. In 2011, it was also ranked as the 2nd largest company in Thailand and the 620th largest company in the world by Forbes 2000.

It was founded under the Royal Decree of King Vajiravudh (King Rama VI) in 1913. Since then, the company has expanded into various businesses with five core business units: chemicals, paper, cement, building materials and distribution. The company is controlled by the Crown Property Bureau, which owns 30% of Siam Cement's shares.

SCG comprises over 100 companies under 5 business groups, employing approximately 24,000 employees, and handling more than 64,000 product items. The products are marketed domestically and exported to all regions of the world. Most companies in the Group have been accredited with ISO 9002 certification for quality management, ISO 14001 certification for environmental management, and TIS 18001 certification for occupation health and safety management, often the first in their respective industries. SCG has also received national and international awards in various areas.