This highly practical troubleshooting guide solves injection molding problems systematically and quickly. The rigorous but user-friendly approach employs the authors' proven »STOP« methodology, considering molding process, mold, machine, and material (4M's) as possible sources of part defects. Importantly, the interaction between tooling, processing, and material is emphasized, allowing successful resolution of difficult problems where »by-the-books« approaches fail. Starting from troubleshooting methodology and tools, there is a focused discussion of key areas impacting troubleshooting, in particular the 4M's, followed by an in-depth troubleshooting guide for various molding defects, structured logically by type of problem / solution. Insightful case studies throughout show the strengths of the STOP method to get real processes to run smoothly and reliably, producing quality