A series of three lessons on the Fourier series is now available in the Fourier Series and Transforms category. The Fourier series plays an important role in representing periodic, continuous-time signals in the frequency domain. These lessons introduce the definition of the Fourier series and the most important Fourier series properties. There is also an entire lesson on the Fourier series of the square wave because of the insight gained and important role of the square wave in Fourier analysis.