Background: Extracellular vesicles are closed structured surrounded by a lipid membrane that are secreted by almost all types of cells; their function is information delivery during cell-to-cell communication. They are most commonly divided into three categories – exosomes, microvesicles and apoptotic bodies. Exosomes are small vesicles with the size of 30–100 nm, and they are found in almost all body fluids, including peripheral blood, urine, breast milk, saliva and others. They are able to deliver their content to target cells and change their behavior. Cancer cells are able to secrete more exosomes and also contain different proteins and RNA species than the exosomes from healthy cells. Due to their specific composition that is connected to the cell of origin, exosomes could be used as biomarkers of various diseases in the future. Purpose: The aim of this work is to summarize current knowledge about exosomes and their role in various processes connected to resistance in tumors.