Radicals are constituent components of Chinese characters. They are structural units that are larger than strokes, i.e., clusters of strokes. This chapter discusses the role that radical components play in the recognition of Chinese characters. We will focus on the question of whether such structural units are also processing units in character recognition. Major paradigms used in previous research include illusory conjunction, lexical decision and naming. Results indicate that a radical level (or sub-character level) exists as a psychological entity. At least in the early stages of processing, characters are probably perceived as radical components rather than as whole characters, propel-ties of radicals, such as their frequency and their position, can affect the speed and/or accuracy of character recognition. Research on sub-character processing is still quite preliminary. After reviewing the existing results, we will point out critical variables that should receive attention and give suggestions for future work.