In this chapter, we will introduce digital watermarking systems and quality evaluation algorithms for audio and speech signals. Originally designed for copyright protection, digital watermarking is a technique that embeds some data to the host signal to show the copyright information. The embedded data, or the watermark, cannot be eliminated from the host signal with normal use or even after some attacks. In the first part of this chapter, we introduce a generic framework of digital watermarking systems. Several properties and application of the watermarking systems are then described. Focused on audio and speech signals, we divide the watermarking algorithms into robust and fragile ones. Different concerns and techniques are described for each category. In the second part of this chapter, a novel watermarking algorithm for audio and speech quality evaluation is introduced together with some conventional quality evaluation standards.