In the process of cheese making, a crucial stage is the coagulation of milk, in which enzymes convert liquid milk into a gel. This process is caused by rennet or other coagulants and involves the aggregation of casein micelles, the main protein component of milk. The presence of additional ingredients like whey proteins and other factors such as pH, temperature, and calcium level can also alter the coagulation process. Specific peptide bonds in κ-casein are hydrolysed by rennet enzymes, especially chymosin, during coagulation, which destabilises casein micelles and causes gel formation next. To formulate the curd, fat globules and whey proteins get ensnared in the resultant gel network. Further influences on milk coagulation characteristics can come from genetic variations in milk proteins, where different forms of κ-casein and other proteins can have favourable or unfavourable effects on coagulation. Important factors influencing cheese quality include the coagulum’s rheological characteristics, such as gel hardness and water-holding ability. For cheese producers to maximise production efficiency and accomplish desired cheese attributes, they must comprehend the coagulation process. The coagulation process in the production of cheese is summarised in this chapter, along with the enzymatic mechanisms involved, important factors influencing coagulation, and consequences for the quality of the cheese.