Milk spoilage is essentially a result of inadequate control of the growth of microorganisms, combined with the activity of enzymes which have found their way into milk from production and processing environments. Microorganisms have developed strategies to survive and thrive in cold (psychrotrophic) as well as in hot (thermophilic) conditions, with some even surviving pasteurization by forming spores. Preventing spoilage is a question of preventing contamination through hygiene and sanitation, proper cooling and understanding the conditions specific to the processes leading to the wide variety of dairy products and ingredients. This chapter examines possible causes of milk spoilage and describes strategies for preventing spoilage during both the production and processing phases. It also examines future trends in this area, including the prospect of better detection and typing methods for identifying problem areas as well as improved technologies for ensuring milk quality all along the value chain.