Calculus III primarily focuses on multivariable calculus, which includes concepts such as partial derivatives, multiple integrals, and vector functions. Key topics covered are the 3-D coordinate system, equations of lines and planes, and functions of several variables, along with their derivatives and integrals. The course also explores advanced integration techniques, including double and triple integrals in various coordinate systems, and the application of theorems like Green's Theorem and Stokes' Theorem. Understanding the gradient vector and its relationship to function behavior is crucial, as is the concept of volumes through slicing for double integrals. Overall, Calculus III extends the principles of differentiation and integration to functions of multiple variables, enhancing the mathematical toolkit for analyzing complex systems.