Carbon Quantum Dots (CQDs) are often modestly referred to as Carbon Dots (CDs). Due to their outstanding opto- and electro-properties, easy accessibility, vast diversity, CQDs have received significant research attention in the past two decades with volumes of studies reporting on their applications in bioimaging, sensing, theranostics, catalysis, light harvesting, antimicrobial amongst others. A major challenge in carbon dots’ research is the morphology control and surface engineering. In this talk, I will use a few of my team’s studies to demonstrate the diverse methodologies to introduce unique functionalities to CDs, from the choice of precursor chemicals, the reaction methods, and to the surface modification. Three case studies will be presented here to demonstrate the various synthesis strategies, the diverse surface functionalities that are attached on CDs, and function as light absorber, or electron donors, or sensory receptors etc. for important applications in photocatalysis and optoelectronic sensors, as well as cancer therapy.