Micro RNAs are small non-coding RNAs that participate in different biological processes, providing subtle combinational regulation of cellular pathways, often by regulating components of signalling pathways. Aberrant expression of mi RNAs is an important factor in the development and progression of disease. The canonical myomi Rs(mi R-1,-133 and-206) are central to the development and health of mammalian skeletal and cardiac muscles, but new findings show they have regulatory roles in the development of other mammalian non-muscle tissues, including nerve, brain structures, adipose and some specialised immunological cells. Moreover, the deregulation of myomi R expression is associated with a variety of different cancers, where typically they have tumor suppressor functions, although examples of an oncogenic role illustrate their diverse function in different cell environments. This review examines the involvement of the related myomi Rs at the crossroads between cell development/tissue regeneration/tissue inflammation responses, and cancer development. Micro RNAs are participating in different biological processes, providing subtle combinational regulation of cellular pathways, often by regulating components of signaling pathways. Aberrant expression of mi RNAs is an important factor in the development and progression of disease. The canonical myomi Rs (mi R-1, -133 and-206) are central to the development and health of mammalian skeletal and cardiac muscles, but new findings show that they have regulatory roles in the development of other mammalian non-muscle tissues, including nerve, brain structures, adipose and some specialized immunological cells. Moreover, the deregulation of myomi R expression is associated with a variety of different cancers, where there they have tumor suppressor functions, though examples of an oncogenic role illustrate their diverse function in different cell environments. This review examines the involvement of the related myomi Rs at the crossroads between cell development / tissue regeneration / tissue inflammation responses, and cancer development.