Genomic imprinting is an epigenetic phenomenon that results in different expression of autosomal genes depending on their parental orgin. Genes can be both paternally and maternally expressed. The mechanisms of this phenomenon include DNA methylation, DNA demethylation and histone modifications. The expression of maternal alleles is mostly achieved by a combination on maternal DNA demethylation and methylation of paternal DNA via different methyltransferases or RNA-dependent DNA methylation pathway. Differences in histone methylation are mainly associated with paternally expressed allels. Small interfering RNAs also participate in the establishment and maintenance of imprintinting on specific sequences. In plants, genes are imprinted mainly in the endosperm. Genes imprinted in the embryo were until now found in A. thaliana and maize, but so far there are only a few candidates and their role is ambiguous. Evolution of imprinting is also unclear and there are several different hypotheses trying to explain it.