Epigenetic regulation of gene enhancer elements is important for establishing 
and maintaining the identity of cells. Gene enhancer elements are thought to 
exist in either active or poised states distinguishable by chromatin features, 
but a complete understanding of the regulation of enhancers is lacking. Here, by 
using mouse embryonic stem cells and their differentiated derivatives, as well 
as terminally differentiated cells, we report the coexistence of multiple, 
defined classes of enhancers that serve distinct cellular functions. 
Specifically, we found that active enhancers can be subclassified based on 
varying levels of H3K4me1, H3K27ac, and H3K36me3 and the pSer2/5 forms of RNA 
polymerase II. The abundance of these histone modifications positively 
correlates with the expression of associated genes and cellular functions 
consistent with the identity of the cell type. Poised enhancers can also be 
subclassified based on presence or absence of H3K27me3 and H3K9me3, 
conservation, genomic location, expression levels of associated genes, and 
predicted function of associated genes. These findings not only refine the 
repertoire of histone modifications at both active and poised gene enhancer 
elements but also raise the possibility that enhancers associated with distinct 
cellular functions are partitioned based on specific combinations of histone 
modifications.