This chapter is a detailed introduction of the imperfective category in general linguistics and the grammatical characteristics of the function word zhe in Standard Mandarin. The impefective usage of zhe in Standard Mandarin is significantly restricted, given that it can only attach to a small subset of verbs and it can only be used with certain types of imperfective viewpoints. I argue that zhe is a homogenous imperfective marker for stage-level events in Standard Mandarin. This chapter defines four basic imperfective meanings in Chinese: the existential resultative, the general resultative, the time-point progressive and the time-stretch progressive. This classification scheme for the imperfective category is essential for understanding the grammatical nature of the aspect marker Zhe in Chinese.