Minute amounts of noncotton fiber impurities that mix with cotton fiber during cotton picking, drying, transportation, and processing are known as cotton foreign fibers. Foreign fibers reduce the cotton grade and affect the quality of cotton processing, causing problems such as stains and uneven dyeing of textile fabrics, leading to quality decline of the final product. Therefore, detecting foreign fiber in cotton is essential. In this paper, we analyze the harm due to foreign fiber in cotton and problems associated with its detection and summarize the foreign fiber-related detection equipment. Simultaneously, a summary of the recent studies and progress in foreign fiber-detection technologies and methods with regard to image segmentation, feature selection, and image classification, and prospects for future research directions is discussed in this paper.