This Topic gives a revision of Trigonometric Fourier Series. It builds on the motivation for using signal decompositions for analysing signals, and decomposes any finite power periodic signal into an infinite summation of sinusoids and cosinusoids, whose frequencies are integer multiples of a fundamental frequency. The Topic gives the formulas for calculating the Fourier coefficient, as well as the Fourier series expansion itself. A graphical example is shown, through decomposing a sawtooth wave, and also provides an audio reconstruction. The second half of the video considers a simple example of calculating the trigonometric Fourier coefficients of a square wave.