MicroRNAs (miRNAs) are tiny noncoding RNAs that have a major regulatory impact on gene expression and are essential for cellular functions like apoptosis, differentiation, and proliferation. A thorough review of the ways that miRNA malfunction affects the development, spread, and metastasis of different cancer types is provided in this chapter. The chapter elucidates the mechanisms underlying miRNA deregulation, including genetic, epigenetic, and transcriptional alterations, and discusses their dualistic function as oncogenes or tumor suppressors. Recent research highlighting key deregulated miRNAs in major cancers is summarized, demonstrating their involvement in hallmark cancer pathways such as cell cycle regulation, apoptosis evasion, and metastasis promotion. Furthermore, the chapter explores the translational potential of targeting miRNA deregulation using novel therapeutics, underscoring the promise of miRNA modulation as a potent strategy in combinatorial cancer therapy. Overall, this chapter provides critical insights into the complex landscape of miRNA deregulation, laying a foundation for innovative, more effective approaches in cancer management.