In-app messaging is a powerful tool for engaging users within a product interface, often used by SaaS companies to guide, educate, or prompt users effectively at moments of interaction. When implemented correctly, it can enhance user activation, feature adoption, and reduce churn by providing timely, personalized prompts that feel more like guidance than marketing. Common formats include banners, cards, and modals, each suited for different levels of visibility and urgency, with successful examples from companies like Linear, Cursor, Loom, Figma, GitHub, Rippling, Notion, Ramp, Airbnb, Dub, and Google Drive illustrating how they can drive user engagement without being intrusive. However, misuse of in-app messaging, such as notification overload or irrelevant targeting, can lead to poor user experiences, highlighting the importance of personalized and contextually-timed communications. Tools like Knock enable teams to create, target, and deploy effective in-app messages that align with their product's logic and design to maintain user engagement.