The Sanlun school, also known as the Three Treatise school, is a Chinese Madhyamaka school that emerged in the sixth century. It is based on the teachings of the Indian Buddhist philosopher Nagarjuna, who is considered the founder of the Madhyamaka school.

The term "Sanlun" is derived from the Chinese translation of the Sanskrit term "Madhyamaka," which means "middle way." This name reflects the school's emphasis on the middle path between the extremes of eternalism and nihilism.

The Sanlun school is primarily based on three key texts, known as the Three Treatises (Sanlun): the Madhyamaka-karika, the Dvadasanikaya-sastra, and the Shata-shastra. These texts are attributed to Nagarjuna and his disciple Aryadeva and are considered the core teachings of the school.

The main focus of the Sanlun school is the concept of emptiness (shunyata). According to this school, all phenomena are empty of inherent existence and are merely conceptual designations. This means that nothing has a fixed or permanent nature and that all things are interdependent and interconnected.

The Sanlun school also emphasizes the concept of the Two Truths, which distinguishes between conventional truth (samvriti-satya) and ultimate truth (paramartha-satya). Conventional truth refers to the everyday reality that we experience, while ultimate truth refers to the ultimate nature of reality, which is emptiness.

In addition to the teachings of Nagarjuna, the Sanlun school also incorporates the teachings of other Madhyamaka masters, such as Buddhapalita and Chandrakirti. It also incorporates elements of Yogacara philosophy, which emphasizes the mind and consciousness.

The Sanlun school had a significant influence on the development of Chinese Buddhism, particularly during the Tang dynasty (618-907 CE). It was also instrumental in the formation of the Tiantai and Huayan schools, which integrated the teachings of the Sanlun school into their own philosophies.

Today, the Sanlun school continues to be an important school of Chinese Buddhism, with many temples and monasteries dedicated to its teachings. Its emphasis on emptiness and the middle way remains relevant and applicable to modern-day practitioners seeking to understand the nature of reality and achieve enlightenment.