Density Functional Theory (DFT) is a widely used electronic structure method due to its balance between computational efficiency and reasonable accuracy. One of the many important choices a user must make when utilizing DFT is that of an appropriate exchange-correlation functional for the system being studied. In this worksheet we will explore the theory underlying two groups of functionals: Generalized Gradient Approximation (GGA) and Meta-Generalized Gradient Approximation (meta-GGA). We will then use two different examples to demonstrate how these functionals perform relative to each other. This worksheet uses the Maple Quantum Chemistry Toolbox.