Continuous variation is the situation encountered where for a given phenotype all values between the two extremes are possible. Examples of this include such things as height and weight. Continuous variation within organisms does not display easily observable states, such as the color of eyes or hair, there is a steady gradation normally observed between the possible extremes.

Continuous variation is sometimes known as quantitative variation. It is common for the characteristic to have a mean value around which the population varies. Continuous variation is most common amongst those characteristics which are strongly affected by environmental factors and also amongst those characteristics which are under the control of many genes acting together. The larger the number of controlling genes the greater is the spread around the mean value.

Continuous variation is found within large populations. In smaller, more isolated communities it can be the case that many of the genes controlling a given character are represented only by one allele per gene (due to inbreeding and genetic drift). This gives the appearance of a characterisitc which is under the control of far fewer genes than is the actual case.