Stem cells are undifferentiated and unspecialized cells that possess properties of self-renewal through mitosis/division and differentiation into many cell types. The sources of stem cells are embryonic stem cells from zygote, bone marrow, peripheral blood and others, but also hypothetically tumors in which cancer stem cells cause metastasis and tumor relapse. Stem cells are divided into embryonic, adult, mesenchymal, induced pluripotent stem cells and a special type of cells – progenitor cells. Depending on their differentiation potential, there are totipotent, pluripotent, multipotent, oligopotent and unipotent stem cells. Cell differentiation is a process in which cell changes from a less specialized type into a more specialized type with certain functions, thus limiting cell differentiation potential. Nuclear reprogramming is the reversal of the differentiation state of a mature cell into one that is characteristic of the undifferentiated embryonic cells, thus creating induced pluripotent stem cells. Yamanaka was the first one to create them in 2006 by transduction of several transcription factors (Oct3 / 4, Sox2, c-Myc and KLF) by viral vector, but there are other methods that do not include manipulation of the genome, such as plasmid transfection and direct delivery of the protein. The success of the reprogramming is based on determining the biological properties of the cell, pluripotency and the reprogramming of epigenetic marks. The use of embryonic stem cells is linked with many ethical issues and the problem of immune rejection, as opposed to induced cells, where the patient's own cells are used, but their disadvantages are the lack of efficiency in production, existing "memory" of somatic origin, and manipulation of the genome causing malignancies. In the basic sciences they are applied in the study of the pathogenesis of various diseases, but also in determining the mechanisms of action and the side effects of new drugs. They are important for the study of normal growth and development and for identifying the causes of congenital anomalies, and their future is their application in the regeneration and complete replacement of damaged tissues and organs.