This video introduces approximating the area under a curve using rectangles. After motivating the subject briefly by comparing the antiderivative to the area under the curve with a nod to the Fundamental Theorem of Calculus, we approximate the area under a curve with 3 rectangles and then with 6 rectangles, noting that 6 gives the better approximation. The video also gives an overview of why using an infinite number of infinitely thin rectangles gives the exact area under the curve.