Mortgage rates fluctuate frequently, making it crucial to lock in the best rate before closing on a home. A rate lock is a written agreement that guarantees a specific interest rate for a set period, typically costing points based on the loan amount. Timing is essential; it's often best to wait until finding a home to lock in a rate. Be cautious of inflated rate caps and consider asking for a float down provision to benefit from falling rates. Ensure all agreements are in writing and be aware that changes in loan type or credit score can affect your locked rate.