This Topic presents the Complex Fourier Series expressions, and provides a physical interpretation of what it means; namely, that a continuous-time period signal can be represented by an infinite summation of complex phasors, whose frequencies are integer multiples of a fundamental. The Topic briefly highlights the concept of a negative frequency, and how pairs of phasors with positive and negative frequencies combine together to give a real signal. The Topic then considers two examples of calculating the Complex Fourier coefficients. The first example has a single functional form over one period, whereas the second example requires the region of integration to be split up.