This chapter presents discussion on atypical squamous cells (ASC). It is the most common interpretation of the cervical cytology. The cervical smear is interpreted as ASC when the cytological features are equivocal and insufficient for the diagnosis of SIL. ASC is a heterogeneous entity and it comprises of both SIL and benign lesions that mimic SIL. In 2001 TBS, ASC is classified into atypical squamous cells of undetermined significance (ASC-US) and ASC-H. There is no provision to report ASC-US favor reactive changes. The criteria of ASC-US are mentioned in this chapter. ASC-H cases are defined as “suggestive of HSIL but fall short of cytological criteria for a definitive interpretation of HSIL”. Liquid-based cytology for ASC-H is also described briefly in this chapter. There are 23 figures also given in this chapter which are very useful for readers.