We investigate the formation of thin current sheets in Earth's magnetotail and the stability of the resulting plasma sheet structure. In the study of current sheet formation we concentrate on the mechanism based on a large gradient of the magnetic flux tube volume and derive a general expression for maximum current density using quasi-static magnetotail theory. That expression relates the amount of magnetic flux transferred to the magnetotail to the maximum current density in the near-Earth tail region. The analysis also includes the effects of varying solar wind plasma pressure and Mach number. The stability analysis addresses the resistive tearing mode, and how the presence of a thin current sheet changes the dispersion relation is investigated. For an infinitely extended double-structured sheet the tearing dispersion curve has a single peak, similar to the dispersion relation of a sheet with a single scale. A qualitative argument suggests that a thin current sheet of finite length might lead to a double-peaked dispersion curve. Several possible consequences of these results are discussed. ¿ 1999 American Geophysical Union