The initiation of the hematopoietic program is orchestrated by key transcription factors that recruit chromatin regulators in order to activate or inhibit blood target gene expression. To generate a complete compendium of chromatin factors that establish the genetic code during developmental hematopoiesis, we conducted a large-scale reverse genetic screen targeting 425 chromatin factors in zebrafish and identified over 30 novel chromatin regulators that function at distinct steps of embryonic hematopoiesis. In vertebrates, developmental hematopoiesis occurs in two waves. During the first and primitive wave, mainly erythrocytes are produced, and we identified at least 15 chromatin factors that decrease or increase formation of \(scl^+\), \(gata1^+\), and \(\beta-globin e3^+\) erythroid progenitors. In the definitive wave, HSCs capable of self-renewal and differentiation into multiple lineages are induced, and we identified at least 18 chromatin factors that decrease or increase the formation of \(c-myb^+\) and \(runx1^+\) stem and progenitor cells in the aorta gonad mesonephros (AGM) region, without disruption of vascular development. The majority of the chromatin factors identified from the screen are involved in histone acetylation, histone methylation, and nucleosome remodeling, the same modifications that are hypothesized to have the most functional impact on the transcriptional status of a gene. Moreover, these factors can be mapped to subunits of chromatin complexes that modify these marks, such as HBO/HAT, HDAC/NuRD, SET1A/MLL, ISWI, and SWI/SNF. One of the strongest phenotypes identified from the screen came from knockdown of chromodomain helicase DNA binding domain 7 (chd7). Morpholino knockdown of chd7 resulted in increased primitive and definitive blood production from the induction of stem and progenitor cells to the differentiation of myeloid and erythroid lineages. This expansion of the blood lineage is cell autonomous as determined by blastula transplantation experiments. Though chromatin factors are believed to function broadly and are often expressed ubiquitously, the combined results of the screen and chd7 analysis show that individual factors have very tissue specific functions. These studies implicate chromatin factors as playing a major role in establishing the programs of gene expression for self-renewal and differentiation of hematopoietic cells.