Epithelial-mesenchymal transition (EMT) is a process whereby epithelial cells gradually transform into mesenchymal-like cells losing their epithelial functionality and characteristics. EMT is thought to be involved in the pathogenesis of numerous lung diseases ranging from developmental disorders and fibrotic tissue remodeling to lung cancer. Lung cancer is the most lethal form of cancer worldwide, and despite significant therapeutic improvements, the patient survival rate still remains low. Activation of EMT endows invasive and metastatic properties upon cancer cells that favor successful colonization of distal target organs. The present review provides a brief insight into the mechanism and biological assessment methods of EMT in lung cancer and summarizes the recent literature highlighting the controversial experimental data and conclusions.