Over the past decade, microRNAs (miRNAs) have become a new paradigm of gene regulation. miRNAs are involved in a wide array of carcinogenic processes. Indeed, increasing evidence has shown the importance of miRNAs in cancer, suggesting their possible use as diagnostic, predictive and prognostic biomarkers, leading to miRNA-based anti-cancer therapies, either alone or in combination with current targeted therapies, with the goal of improving cancer treatment responses and increasing cure rates. The advantage of using a miRNA approach is based on the ability to concurrently target multiple effectors of pathways involved in cell proliferation, migration and survival. This review sheds new light on miRNA regulation of genes that play critical roles in the process of malignant transformation and tumour metastasis, the dysregulation of miRNA expression in cancer development and the development of miRNA-based diagnostics and therapeutics.