Within the active field of in vitro digestion in food research, the COST Action INFOGEST aimed to harmonizein vitro protocols simulating human digestion on the basis of physiologically inferred conditions. A harmonizedstatic in vitro digestion (IVD) method was recently published as a primary output from this network. To validatethis protocol, inter-laboratory trials were conducted within the INFOGEST network. A first study was performedusing skim milk powder (SMP) as a model food and served to compare the different in-house digestion protocolsused among the INFOGEST members. In a second inter-laboratory study applying the harmonized protocol, thedegree of consistency in protein hydrolysis was investigated. Analysis of the hydrolyzed proteins, after the gastric and intestinal phases, showed that caseins were mainly hydrolyzed during the gastric phase, whereas β-lactoglobulin was, as previously shown, resistant to pepsin. Moreover, generation of free amino acids occurredmainly during the intestinal phase.The study also showed that a few critical steps were responsible for the remaining inter-laboratory variability.The largest deviations arose from the determination of pepsin activity. Therefore, this step was further clarified,harmonized, and implemented in a third inter-laboratory study.The presentwork gives an overviewof all three inter-laboratory studies, showing that the IVD INFOGEST methodhas led to an increased consistency that enables a better comparability of in vitro digestion studies in the future.