Cancer is considered as the leading cause of death and the major barrier of longevity globally. The high mortality of cancer is due to the malignant spread. However, if the disease could be identified at an early stage, treatment like resection and proper therapies will extend the life of patients. Unfortunately, the current early detection methods are facing limitations, such as the lack of sensitivity and specificity, overdiagnosis, high risk of infection, as well as labor-intensive. Therefore, a set of effective strategies for cancer screening and early diagnosis is highly in demand. Circulating tumor cells (CTCs) are a small number of tumor cells shed from the primary sites and transferred to the metastatic foci through the circulatory system. They not only provide comprehensive information about the heterogeneous tumor in a non-invasive and easy way, but also offer great potential as novel biomarkers for liquid biopsy in early cancer detection. Here, we overview the biological characteristics of CTC and introduce several commercially available technologies for CTC capture. Additionally, we will discuss the differences of the CTC-based approach and the traditional early diagnostic methods. To sum up, this chapter focuses on the current state of knowledge on CTCs and aims to explore possibilities for the early detection of human cancers.