A back pressure valve for providing a double barrier to flow for use with a tubing hanger within a well bore, wherein the back pressure valve can have a first body piece threadably engaged and sealed with a second body piece. A first piston can engage a first surface for sealing bottom pressure to provide a first barrier to flow. A second piston can engage a second surface for redundantly sealing bottom pressure to provide a second barrier to flow. The back pressure valve can have one-way and two-way back pressure valve assemblies. The two-way back pressure valve assembly can include a bidirectional piston having a double sealing face for engaging sealing surfaces and sealing bottom pressure from the well bore while allowing testing without stopping a flow of fluid.