In Chapter 5, we introduced how a periodic signal defined for /< t</ or a signal defined in a closed time interval a t b can be expanded in a Fourier series, i.e., how it can be expressed as a linear combination of infinite sinusoidal signals. The Fourier series expansion reveals the frequency content of a signal. In this chapter, we introduce a generalized concept that expresses in the frequency domain (almost), any signal defined in the time domain for /< t</. The Fourier transform is the way to express in the frequency domain a signal that is given in the time domain. In this chapter, we discuss the Fourier transform of continuous-time signals, which is known as continuoustime Fourier transform (CTFT). By applying Fourier transform to a continuous-time signal x(t), we obtain a representation of the signal at the cyclic frequency domain V or equivalently at the frequency domain, f.