The human pathogen Helicobacter pylori causes inflammation in the stomach of infected hosts, leading in some cases to the development of gastric cancer. Several mouse models have been developed to study Helicobacter-induced carcinogenesis with similarities to gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma (MALToma) in humans. These models require chronic infection of animals with mouse-colonizing isolates of H. pylori or with related gastric Helicobacter spp., such as the canine/feline species Helicobacter felis. Furthermore, consistent with the known influence of host and environmental factors in human gastric cancer, it is possible to manipulate the type and severity of gastric lesions in mouse Helicobacter infection models through the use of different mouse genetic backgrounds and/or by the administration of known cocarcinogens, such as alkylating agents (e.g., N-nitroso-N-methylurea), or even elevated quantities of dietary salt. Here, we describe protocols for the inoculation of mice with gastric Helicobacter spp. and the administration of these cocarcinogens. Furthermore, we will describe the various methodologies used to study gastric inflammation and carcinogenesis in Helicobacter-infected animals. © 2012 Springer Science+Business Media, LLC.