Since its development in the early 2000’s, 787-mm tall W-beam guardrail, commonly referred to as the Midwest Guardrail System (MGS), has proven to be one of the most versatile and robust roadside barrier systems in use today. The MGS is typically configured as a strong-post system utilizing either W6 × 8.5 steel posts or 152 mm × 203 mm wood posts. However, multiple weak-post MGS configurations have been developed using S3 × 5.7 steel posts. These weak-post systems absorb energy through post bending instead of post rotation through soil, so they are favored in various special applications such as bridge rails, culvert mounted systems, and placement within pavements or mow strips. These weak-post guardrail systems are non-proprietary and can be used by roadway agencies all around the world. This paper contains details and drawings encompassing various weak-post MGS configurations that have been developed and evaluated to the American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH) safety standards. The systems are discussed in terms of key components and performance characteristics, such as test level and working width. Finally, implementation guidance is provided for the proper layout and installation of the weak-post MGS configurations.