Phenotypic variation is influenced by both genetic and environmental variation. One important source of environmental variation is the maternal effect: influences of the maternal environment on offspring phenotype. Heritable maternal effects have been shown to influence the life histories, behaviour, and population dynamics of a wide variety of plants and animals. They are likely to have evolved as a mechanism for cueing offspring to appropriate development for predicted environmental conditions. This will be the first book dealing with the broad range of maternal effects.