The immune system consists of a diverse range of cell types, each performing its specific function. T-lymphocytes, B-lymphocytes, and NK (natural killer) cells provide protection against infections and tumors and participate in the regulation of immune responses. Disorders in the development and function of lymphocytes can lead to various immunodeficiencies, autoimmune diseases, and oncological conditions. The functional and morphological diversity of the B- and T-cell immune system in health and disease is maintained by dynamic genetic and epigenetic changes, including those mediated by small regulatory molecules-microRNAs (miRNAs). This review presents current data on the role of miRNAs in the development of B- and T-cells, their activation, and malignant transformation. Aberrant expression of miRNAs plays a key pathogenic role in the development and maintenance of lymphomas, characterizing them as promising diagnostic and prognostic markers.