Very little is known about the extinct mammals and how many extant mammals are found in Eritrea. Data have been gathered with the objectives of clearly defining the extinct, extirpated and endangered mammals in Eritrea. Findings indicate that seventeen taxa of fossil and subfossil mammals in six orders were found in Eritrea, extending from the late Oligocene to the Holocene. Faunal correlation among paleontological sites in the Horn of Africa and East Africa indicate that the best close correlation are the Haïdalo site in Djibouti and the Chilga site in Ethiopia. Provisional findings on extant mammals indicate that for its small size, Eritrea is extremely diverse; it is predicted that similar species richness would be found for fossil fauna. Of the 132 species of mammals known from Eritrea, 114 are terrestrial. Of these, 71.1% of species are small mammals (less then 10 kg adult body mass), 73.7% are nocturnal, and about 21.9% are fossorial, a possible explanation why they survived hunting and the 30-year war between Ethiopia and Eritrea. It has been postulated that the center of evolution of some small mammal taxa might have been in Ethiopia; this hypothesis should be tested for Eritrea. The 11 extirpated and 8 endangered mammals in Eritrea are listed. From the 3rd century BC until the 20th century AD, elephants were sighted in areas where they are not found today. The observation of more than 28 elephants by Shoshani and colleagues in 2001 was a rare phenomenon for Eritrea; the previous last sighting of a large herd was 46 years ago. In 2003 at least 83 elephants were also observed. Elephants (Loxodonta africana) in Eritrea are endangered; being very large and a keystone species, protecting them would also preserve other animals and plants in the same ecosystem. The symbiotic relationship between elephants and doum palms is critical to the survival of these two species. Conservation programs must include public awareness and education, emphasizing the role animals play in a balanced nature. Protecting the unique natural heritage of Eritrea is an asset to be promoted through ecotourism for this and future generations. This report is the first combined account on the extinct and extant mammalian fauna of Eritrea. Prior to 1993 all publications concerning faunal assemblages from Eritrea were under the heading of Ethiopia, since Eritrea was a province of Ethiopia. Data presented here, it is hoped, will serve as a basis for future research on the paleozoogeography and neozoogeography of Eritrean mammals.