The book probes into the use of English RCs by Chinese college students of three English proficiency levels.It is found that the Chinese students use fewer RCs and make more errors compared with English native students due to three reasons: interlingual factors, intralingual factors and language universal properties. Moreover,the English proficiency level is proved to be an important parameter in the use of English RCs. It not only influences the number of RCs the Chinese students use, but also determines the variety of RCs and the number and variety of errors they make.The book can enrich the literature on the English RC acquisition of ESL and EFL learners.