Package integrity is an essential requirement for the high quality of modified-atmosphere packaged (MAP) food. The most effective method of detecting a leakage non-destructively throughout the whole distribution chain from the manufacturer to the consumer is to use a visual leak indicator that is permanently attached to the package. This article reviews visual leak indicators that are based on the detection of oxygen and carbon dioxide. The limitations and benefits of the current indicator technologies are discussed. Commercial indicators and the problems associated with their adoption, as well as the safety aspects of indicators, are also introduced.