MongoDB performance often comes down to one thing, indexing done right. This post breaks down practical MongoDB indexing strategies that improve query speed, reduce CPU load, and help databases scale cleanly as data grows. It covers where indexes help, where they hurt, and how to choose the right type for your query patterns, including single field, compound, and partial indexes. It also touches on common mistakes like over indexing, indexing fields with low selectivity, and ignoring sort and range behavior. If your app feels fast in development but slows down in production, this is the place to start.