How do I handle disagreement with my engineering manager about technical decisions?

This is where duty and clarity meet, and it's uncomfortable. I've had to tell leaders things they didn't want to hear, and I've been the one resisting feedback I needed. First, disagree with the decision, not the person. Study the facts until you're sure. "I think we should reconsider the material choice" is very different from "that's a bad call." One opens a conversation. The other puts people on the defensive. Second, pick your moment. Not in front of the team, not when everyone's heated. Ask for a focused talk. Bring options, not just complaints. "Here's why I'm concerned, and here's what I'd do instead" shows you've thought it through. Third, be willing to be wrong. The best outcome is you learn something. The next best is your manager rethinks it. Both make the work better. If after a real conversation you still disagree on something fundamental, like safety or a plan you believe won't work, then escalate it or put your concern in writing. That's not going behind anyone's back. That's professionalism. But most disagreements are smaller than that, and most get solved with respect and clarity. Lead with both.