The PHD finger is a Zn-binding domain found in all eukaryotic genomes, and typically show a C4HC3 signature. Notably, many if not all PHD fingers are found in nuclear proteins whose functions are associated with the regulation of transcription, cell cycle and apoptosis. Increasingly evidences suggest that the PHD finger has multiple functions, including the protein-protein interaction, especially interact with nucleosomes. The pattern and combination of histone modifications, for example, methylation, acetylation, phosphorylation and ubiquitination etc, have been believed to be an important regulator of gene expression and state of the chromatin, which have raised the histone code hypothesis. With the feature of specific recognizing methylated histone, the PHD finger may functions as an important reader of the histone code.