In this book, the fundamental problems and techniques of echo and noise cancellation are introduced. Acoustic echo cancellation is disturbed by both far-end and near-end speeches. We propose a new algorithm to reduce the far-end speech interference. To avoid the near-end interference, a new double-talk detection method is proposed. Computer simulation shows the proposed method is effective. Active noise control (ANC) involves the determination of the impulse responses between the sources and sensors. We first modify the commonly used three-dimensional image method in a duct and ANC model is established. We examine its sensors number and locations as well as noise reduction performance.