The Ghent Altarpiece, also called the Adoration of the Mystic Lamb, is a very large and complex 15th-century polyptych altarpiece in St Bavo's Cathedral, Ghent, Belgium. It was begun around the mid-1420s and completed by 1432, and it is attributed to the Early Netherlandish painters and brothers Hubert and Jan van Eyck. The altarpiece is a prominent example of the transition from Middle Age to Renaissance art and is considered a masterpiece of European art, identified by some as "the first major oil painting."

An altarpiece is an work of art in painting, sculpture or relief representing a religious subject made for placing at the back of or behind the altar of a Christian church. Though most commonly used for a single work of art such as a painting or sculpture, or a set of them, the word can also be used of the whole ensemble behind an altar, otherwise known as a reredos, including what is often an elaborate frame for the central image or images. Altarpieces were one of the most important products of Christian art especially from the late Middle Ages to the era of Baroque painting.