Current sheets in MHD turbulence

Current sheets may be the origin of fast dissipation rates in many MHD systems. The structure, formation and destruction of current sheets in force free MHD turbulence is reviewed. Special attention is given to the topological constraints that limit the possible sites of current sheets. The importance of field lines that form closed loops, including null-null loops, and the current sheets that form on them is discussed. In many situations the MHD approximation describes the plasma away from the current sheets but not in the immediate vicinity of the sheets. The plasma processes operating in the sheets are considered briefly.