This handbook (in 4 volumes) investigates important tools for empirical and theoretical research in finance and accounting. Based on editors' and contributors' years of experience working in the industry, teaching classes, conducting research, writing textbooks, and editing journals on the subject of financial econometrics, mathematics, statistics, and technology, this handbook will review, discuss, and integrate theoretical, methodological, and practical issues of financial econometrics, mathematics, statistics, and machine learning.