We propose an analytic framework to study the nonperturbative solutions of Witten's open string field theory. The method is based on the Moyal star formulation where the kinetic term can be split into two parts. The first one describes the spectrum of two identical half strings which are independent from each other. The second one, which we call midpoint correction, shifts the half string spectrum to that of the standard open string. We show that the nonlinear equation of motion of string field theory is exactly solvable at zeroth order in the midpoint correction. An infinite number of solutions are classified in terms of projection operators. Among them, there exists only one stable solution which is identical to the standard butterfly state. We include the effect of the midpoint correction around each exact zeroth order solution as a perturbation expansion which can be formally summed to the complete exact solution.Recently, this formal correspondence played a major rôle in importing basic ideas of noncommutative geometry to string field theory. One of the stimulating ideas is the vacuum string field theory (VSFT) proposal [3]. With an assumption on a simplified kinetic term to describe the tachyon vacuum, the classical solutions that would describe the D-brane are given by the noncommutative soliton [4] (=projector). It is well known that projectors are the fundamental geometrical objects in noncommutative geometry since they represent the K-homology group. The proof of the VSFT conjecture on the kinetic term was, however, difficult and there remained many open questions.The kinetic term is given by the Virasoro operator which is a second order differential operator acting on string fields A x, ξ, ξ gh . We specify this operator later since it will be