Urie Bronfenbrenner was an American psychologist best known for developing the Ecological Systems Theory. This theory emphasizes the different layers of environment that influence human development, ranging from immediate settings like family and school to broader contexts like culture and society. Bronfenbrenner's model includes several systems: the microsystem (immediate environment), the mesosystem (interconnections between microsystems), the exosystem (external environments affecting the individual), and the macrosystem (cultural and societal influences). His work highlights the importance of considering these various contexts when studying human behavior and development.