"Summa de Arithmetica, Geometria, Proportioni et Proportionalita" is a comprehensive mathematical work by Leonardo of Pisa, also known as Fibonacci, published in 1202. This book covers various topics, including arithmetic, geometry, and the principles of proportion, making it a foundational text in the development of mathematics in Europe. The work is notable for introducing the Fibonacci sequence, a series of numbers where each number is the sum of the two preceding ones. It also emphasizes practical applications of mathematics, such as in commerce and trade, significantly influencing mathematical thought and education during the Middle Ages.