The existence of cancer stem cells is debatable in numerous solid tumors, yet in leukemia, there is compelling evidence of this cell population. Leukemic stem cells (LSCs) are altered cells in which accumulating genetic and/or epigenetic alterations occur, resulting in the transition between the normal, preleukemic, and leukemic status. These cells do not follow the normal differentiation program; they are arrested in a primitive state but with high proliferation potential, generating undifferentiated blast accumulation and a lack of a mature cell population. The identification of LSCs might guide stem cell biology research and provide key points of distinction between these cells and their normal counterparts. The identification and characterization of the main features of LSCs can be useful as tools for diagnosis and treatment. In this context, the aim of the present review was to connect immunophenotype data in the main types of leukemia to further guide technical improvements.