The knowledge that miRNA expression is frequently dysregulated in cancer has uncovered an entirely new repertoire of molecular factors upstream of gene expression, with exciting potential as novel biomarkers and therapeutic targets in cancer. Exploiting the unique characteristics of these molecules including their stability, tissue specificity, ease of detection and manipulation, will bring clinicians ever closer to achieving the goal of individualized cancer treatment. We present a comprehensive and timely review of the role of miRNAs in cancer. Herein we address briefly miRNA biogenesis, the putative role of miRNAs as oncogenes or tumor suppressors, and their potential as sensitive and specific tumor markers with particular emphasis on the commonest cancers; breast, prostate, lung and colorectal. We also discuss circulating tumor-associated miRNAs which are emerging as clinically useful tools for early detection, prognostication and management of various cancers. Finally we explore their potential therapeutic applications in the field of cancer and highlight some of the potential challenges that need to be overcome in order to bring miRNAs from bench to bedside. Given the evidence to date, we envisage a pivotal role for miRNAs in the future individualized management of cancer patients.