Lean manufacturing focuses on eliminating waste in processes to reduce costs and shorten cycle times. It aims to understand what adds value from the customer's perspective. Non-value added activities that are necessary are considered "necessary waste". Implementing lean requires overcoming roadblocks like lack of time, budget or belief that it won't work for a particular organization. Key lean tools include 5S, visual controls, kaizen, value streams, pull systems, mistake proofing, quick changeovers, six sigma, and the theory of constraints.