 The study of quantitative or continuous traits can be carried out by looking simply at phenotypes. For example, if a population of plants varies in height we can ask how much of this variation is due to genes. Assessing the proportion of the variation of a trait in a population that is due to genes is achieved by a statistical method called the analysis of variance. Once this analysis has been carried out a simple formula provides a number between 0 and 1 that is the heritability measure for the trait in question. We use a few simple examples to illustrate the important concepts involved in producing heritability measures.