The article discusses the importance of evaluating the preservation of network modules across different conditions or datasets. The authors introduce several module preservation statistics that do not require a module assignment in the test network, distinguishing between statistics defined for general networks and those for correlation networks. They demonstrate that the correlation structure facilitates the definition of powerful module preservation statistics. The study highlights that module preservation is different from cluster preservation and suggests aggregating multiple preservation statistics into summary statistics for better evaluation. The methods are applied to six gene co-expression network applications, including the preservation of cholesterol biosynthesis pathways, comparison of human and chimpanzee brain networks, and sex differences in cortical and liver networks. The results show that apoptosis genes differ in co-expression between humans and chimpanzees, and several human cortical modules are less preserved in chimpanzees. The article also includes simulation studies and provides data, R software, and tutorials for reproducibility.The article discusses the importance of evaluating the preservation of network modules across different conditions or datasets. The authors introduce several module preservation statistics that do not require a module assignment in the test network, distinguishing between statistics defined for general networks and those for correlation networks. They demonstrate that the correlation structure facilitates the definition of powerful module preservation statistics. The study highlights that module preservation is different from cluster preservation and suggests aggregating multiple preservation statistics into summary statistics for better evaluation. The methods are applied to six gene co-expression network applications, including the preservation of cholesterol biosynthesis pathways, comparison of human and chimpanzee brain networks, and sex differences in cortical and liver networks. The results show that apoptosis genes differ in co-expression between humans and chimpanzees, and several human cortical modules are less preserved in chimpanzees. The article also includes simulation studies and provides data, R software, and tutorials for reproducibility.