This chapter presents the force method, which solves the problem of analysis of elastic statically indeterminate bar systems. This method was introduced by James C. Maxwell in 1864 and refined at the end of the 19th century. The chapter distinguishes external static indeterminacy of a bar system when support reactions are not determined from equations of statics. It distinguishes internal static indeterminacy when, under some support reactions, the equations of statics determine reactions of other constraints ambiguously. Static indeterminacy is caused by redundant or extra connections. The force method is developed by means of a statically indeterminate primary system without any changes in equations and design formulas.