With the advent of social robots which are designed to be 'social', human-like interactions have become a necessity. It is natural for us to use a plethora of emotions to convey additional information or to make an interaction more engaging. But emotion expression is not commonly associated with robots. Many humanoid robots cannot generate facial expressions to portray various emotions. Studies have shown that robots are multi-modal systems which can employ multiple channels to express an emotion. This thesis explores the non-verbal emotion expression techniques and their expressive capabilities. We found that some emotions are easier to express than others, and a single technique cannot express all the emotions. We chose a few emotions and systematically determined the best technique for each of them.