The data mining and machine learning literature currently lacks a unified treatment of multi-label dimensionality reduction that incorporates both algorithmic developments and applications. Addressing this shortfall, this book covers the methodological developments, theoretical properties, computational aspects, and applications of many multi-label dimensionality reduction algorithms, including existing dimensionality reduction algorithms and new developments of traditional algorithms. It illustrates how to apply the algorithms to solve real-world problems. A supplementary website provides a MATLAB package for implementing popular dimensionality reduction algorithms.