【Abstract】Emergent behaviors of complex systems have fascinated mankind for aeons. It is only in recent decades that extensive efforts have been made to quantitatively study them, resulting in important theories and tools such as chaos theory, random fractal theory, and multiscale analyses. This talk aims to convey the best practices in this vast field, emphasizing theory meets reality. As illustrative examples, river flow dynamics, brain dynamics, financial crises, and world-wide political conflicts will be briefly discussed.