Yin Yang 1 (YY1) is a multifunctional protein regulating both gene transcription and protein modifications. Recent studies reveal a proliferative role of YY1 in oncogenesis. Consistently, YY1 overexpression has been observed in various human malignancies and its levels correlate with poor prognoses of many types of cancers. In this review, we focus on the signaling pathways and regulatory proteins that YY1 modulates to promote tumor cell growth, proliferation, migration and metastasis. We also discuss the signals and molecules that regulate YY1 expression and function in cancer-related context. Based on the expression feature and regulatory activities in tumor cells, YY1 possesses a great potential as a biomarker for many cancers and can serve as a therapeutic target clinically to impede cancer development and progression or sensitize cancer cells to anticancer drugs.