The discrete-time Fourier transform (DTFT) is the tool of choice for frequency domain analysis of discrete-time signals and signal-processing systems. In this lesson you will learn the definition of the DTFT and how to evaluate the DTFT of several common signals. You will also build your intuition for the relationships between time and frequency domain descriptions of discrete-time signals. A significant portion of discrete-time signal-processing theory and applications are based on the foundation provided in this lesson.