Mammalian SWI/SNF or BAF chromatin‐remodeling complexes are polymorphic assemblies of homologous subunit families that remodel nucleosomes. BAF57 is a subunit of the BAF complexes; it is encoded only in higher eukaryotes and is present in all mammalian assemblies. Its main structural feature is a high‐mobility group domain, the DNA‐binding properties of which suggest that BAF57 may play topological roles as the BAF complex enters or exits the nucleosome. BAF57 displays specific interactions with a number of proteins outside the BAF complex. Through these interactions, it can accomplish specific functions. In the embryo, BAF57 is responsible for the silencing of the CD4 gene during T‐cell differentiation, and during the repression of neuronal genes in non‐neuronal cells, BAF57 interacts with the transcriptional corepressor, Co‐REST, and facilitates repression. Extensive work has demonstrated a specific role of BAF57 in regulating the interactions between BAF and nuclear hormone receptors. Despite its involvement in oncogenic pathways, new generation sequencing studies do not support a prominent role for BAF57 in the initiation of cancer. On the other hand, evidence has emerged to support a role for BAF57 as a metastasis factor, a prognosis marker and a therapeutic target. In humans, BAF57 is associated with disease, as mutations in this gene predispose to important congenital disorders, including menigioma disease or the Coffin–Siris syndrome. In this article, we present an exhaustive analysis of the BAF57 molecular and biochemical properties, cellular functions, loss‐of‐function phenotypes in living organisms and pathological manifestations in cases of human mutations.