In this chapter we compare the development, characteristics, validity and reliability of two widely used quality of life (QOL) assessment tools in lung cancer: the EORTC QLQLC13 and the FACT-L. The authors found that both questionnaires were developed from input of patients and health care professionals. The QLQ-LC13 is a 13-item instrument that assesses coughing, hemoptysis, dyspnea and pain and the side effects of treatment. Two international field studies have concluded that the QLQ-LC13 is clinically valid and useful. Conversely, the FACT-L assesses general QOL and seven lung cancer-specific items, such as shortness of breath, weight loss, cough, and appetite. In a study of 116 lung cancer patients, the FACT-L was found to have a good internal consistency, reliability, and sensitivity to changes in performance status. Ultimately, both the EORTC QLQ-LC13 and the FACT-L have been sufficiently validated; as such, decision-making should depend on the needs of the investigation.