This paper includes laboratory and field measurements of maximum wave amplitudes of irregular waves. Few measurements of maximum irregular wave heights have been available previously, and the results in this paper will aid in evaluating limiting wave proportions. The data in section 2 of this paper cover observations of breaking waves in a laboratory irregular wave system and results for the largest waves in field observations for severe weather conditions in the North Atlantic. The data are compared with theoretical predictions based on the assumption that wave breaking is the predominant factor limiting wave height. These results may be used to estimate maximum wave conditions for design purposes when field data for maximum wave conditions are not available. Differences in wave spectra for equilibrium wave conditions are investigated in section 3, and it is concluded that the proportion of breaking waves in an irregular wave record explains the variations observed.