Lung cancer–related mortality is the most common cause of cancer death worldwide. Detecting lung cancer at an earlier stage and, ideally, predicting who will develop the disease and particularly the most aggressive forms of cancer are the biggest challenge. MicroRNAs (miRNAs) are short, noncoding RNA molecules with regulatory function on protein-coding genes. Because of their fundamental role in development and differentiation, their involvement in the biological mechanisms underlying tumorigenesis, as well as their low complexity, stability, and easy detection, they represent a promising class of tissue-and blood-based biomarkers of cancer. We summarize the current literature on the use of microRNAs as diagnostic and prognostic tools in lung cancer and discuss the relevant clinical implications of these findings.