The Eight Trigrams form the foundation of the I Ching, consisting of eight basic symbols, each composed of three lines (either broken yin lines or solid yang lines). These eight trigrams represent eight fundamental phenomena and attributes of the natural world and human society, serving as an essential tool for ancient people to understand and interpret the world.

The Qian Trigram (☰), composed of three solid yang lines, represents heaven, the father, strength, and creativity. The Kun Trigram (☷), composed of three broken yin lines, represents earth, the mother, gentleness, and receptivity. These two trigrams are regarded as the "parent trigrams," while the other six trigrams are considered "child trigrams," generated through the interaction of Qian and Kun.

The Zhen Trigram (☳) symbolizes thunder, representing vibration and action, and corresponds to the eldest son in the family. The Xun Trigram (☴) symbolizes wind, representing penetration and entry, and corresponds to the eldest daughter. The Kan Trigram (☵) symbolizes water, representing danger and flow, and corresponds to the middle son. The Li Trigram (☲) symbolizes fire, representing brightness and attachment, and corresponds to the middle daughter.

The Gen Trigram (☶) symbolizes mountain, representing stillness and obstruction, and corresponds to the youngest son. The Dui Trigram (☱) symbolizes lake, representing joy and communication, and corresponds to the youngest daughter. These eight trigrams broadly encompass the primary phenomena and relationships in the natural world and human society.

The arrangement of the trigrams' directions is also clearly documented in the I Ching. The Earlier Heaven arrangement, attributed to Fu Xi, positions Qian in the south, Kun in the north, Li in the east, Kan in the west, Dui in the southeast, Zhen in the northeast, Xun in the southwest, and Gen in the northwest. The Later Heaven arrangement, developed by King Wen of Zhou, differs in orientation and places greater emphasis on practical application.

There are many methods for memorizing the trigram symbols. Zhu Xi, in his "Zhou Yi Ben Yi," composed a mnemonic song for the trigrams: "Qian three unbroken, Kun six broken; Zhen like an upturned bowl, Gen like an inverted bowl; Li hollow in the center, Kan full in the center; Dui broken above, Xun broken below." Through this simple and memorable rhyme, beginners can quickly grasp the basic forms of the trigrams. Understanding the trigrams opens the door to the wisdom of the I Ching.