We develop an inverse scattering transform formalism for the "good " Boussinesq equation on the line. Assuming that the solution exists, we show that it can be expressed in terms of the solution of a 3 x 3 matrix Riemann-Hilbert problem. The Riemann-Hilbert problem is formulated in terms of two reflection coefficients whose definitions involve only the initial data, and it has a form which makes it suitable for the evaluation of long-time asymptotics via Deift-Zhou steepest descent arguments.