Quality is the key to compete and to retain customers. The goal of service quality is very simple - customer satisfaction. High levels of repeat customers lead to high levels of profit. Many companies find 20 percent of their customers provide over 80 percent of their revenue. These are repeat customers. Customer retention is at the heart of profitable companies. How can we achieve quality or in other words customer satisfaction? The International standard of ISO may help companies to close the gap of customer's un-satisfaction though it is somehow subjective and hard to define what quality is? Nowadays, the ISO standards represent the common denominator of business quality that is accepted internationally. Up to the end of December 2002, at least 561,747 certificates of conformity to ISO 9000 standards had been issued in 159 countries (www.iso.ch). The ISO 9000 standards were adopted by the International Organization for Standardization (ISO) in the year of 1987. ISO certification demonstrates the capability of a supplier to control the process that determine the acceptability of the product or service being supplied. We have now entered a period of geometric growth in the number of operations achieving certification. One can expect that when a certified supplier is competing with a non-certified supplier, the certified one will be preferred. In this study, I would like to elaborate the working understanding of ISO 9000, its requirements and methodologies for compliance. By means of the case study - Securicor Macau, hoping this study can help managers to understand the principle of ISO 9000 and sharing the experience in the application of ISO 9000 certificate. In the literature review, definition of quality has been discussed, Garvin comes with his five main approaches of quality: The transcendent based; the product-based, the consumer-based; the producer-based and the value-based. Garvin also identify the eight dimensions of quality: performance; features; conformance; durability; serviceability; aesthetics; perceived quality. These dimensions can be independent or interrelated to each others. And it is important to acknowledge the customer's view point in the end. Edward Deming, Joseph Juran, Kaoru Ishikawa, Philip Crosby are the gurus of quality. All of them have their own thoughts and methods in quality management. Though their approaches in quality may be different, however they all have the same desired goal in terms of quality. In ISO 9000:2000, the eight quality management principles: customer focus; leadership; involvement of people; process approach; system approach to management; continual improvement; factual approach to decision making; and mutually beneficial supplier relationships; are the framework to guide organizations for quality improvement. The Deming circle - plan, do, check, act concept is deployed in the process approach, which help maintaining and continually improving the process capability at all levels within the organization. In the case study, Securicor Macau a leading security service provider in Macau. The strong competition of the market has led to the company to deploy ISO as a strategy to maintain it competitiveness. During the process of ISO adoption, difficulties such as resistance to change, work process design and the enforcement of ISO application were found in the case study. Finally, there are recommendations which might useful for Managers or readers throughout the process of ISO adoption.