Grothendieck Theory refers to the mathematical framework developed by the French mathematician Alexander Grothendieck in the mid-20th century, primarily in the field of algebraic geometry. It revolutionized the study of geometric objects by introducing concepts such as schemes, functors, and topoi, allowing mathematicians to work with more abstract structures and relationships. This theory emphasizes the importance of understanding the underlying properties of mathematical objects rather than just their specific forms. Grothendieck's work laid the foundation for many modern developments in mathematics, influencing areas like number theory, category theory, and homological algebra.