MicroRNAs (miRNAs) comprise an important class of small single-stranded non-coding RNAs that regulate several important biological processes, including cell differentiation, growth, and apoptosis. The dysregulations of miRNAs are usually correlated with several diseases because of their regulatory functions in organisms. Over the past few years, miRNAs are often observed to be aberrantly expressed in cancers, indicating their potential correlations with cancer pathogenesis. Recently, evidence has increased to prove this assumption. Further investigations show that miRNAs are involved extensively in various cancer cell processes on the molecular level, including promotions of cancer cell development. Considering the important functions of miRNAs in cancer development, investigating the relationship between miRNAs and cancers can lead to a better understanding of the latter. Therefore, this review summarizes recent developments from related studies, particularly focusing on the functions of miRNAs and their potential applications as therapeutic strategies for cancers.