The aetiology of multiple sclerosis remains incompletely understood. In patients occurs both demyelination, inflammation, axonal damage and oligodendrocytes degeneration. The changes affect both white and grey matter, and also has been shown in normal appearing grey and white matter. However, it is well established that the immune system directly participates in the destruction of myelin and nervous cells and numerous abnormalities on the cellular and humoral response both in blood and cerebrospinal fluid were found in multiple sclerosis patients. The mechanisms leading to damage of the central nervous system are multifactorial. T lymphocytes play the key role, but B lymphocytes, macrophages and microglial cells are also included. Moreover, neurotoxic agents and metabolic disorders may lead to a direct damage of the central nervous system. The paper presents results of recent studies on the immunopathogenesis of multiple sclerosis and the various stages leading to damage to the central nervous system are discussed: the role of the activation of lymphocytes and antigen presenting cells both in blood and in the central nervous system, pass through the blood–brain barrier, the role of T cells and their respective subpopulations (Th1, Th2, and Th17), the importance of B cells, antibodies and the complement system and the mechanisms of demyelination and axonal damage. At the same time are discussed how drugs used in multiple sclerosis therapy affect different stages of the multiple sclerosis aetiopathogenesis, taking into account also the drugs which are at the clinical trials.