Long-beaked echidnas (Zaglossus), which are endemic to New Guinea, are the largest and least-studied of the 3 extant genera of monotremes. Zaglossus is listed as endangered by the World Conservation Union and data regarding the natural history of long-beaked echidnas are critical to efforts to protect these animals. However, no detailed studies of the ecology of this genus have been published. From 2000 to 2005, I captured 22 Zaglossus bartoni in the Crater Mountain Wildlife Management Area in Simbu Province, Papua New Guinea. Mean body masses for these animals were 6.5 kg ± 1.4 SD (n = 15, range: 4.2–9.1 kg) for adults and 4.3 ± 7.4 kg (n = 6, range: 3.2–5.1 kg) for juveniles. Eleven of the adults captured were followed via radiotelemetry for 1–12 months. The home ranges for these individuals varied in size from 10 to 168 ha. Home-range size was not correlated with body mass, age, or sex. Long-beaked echidna dens were most commonly located in underground burrows, although individual echidnas favored different types of den sites. Mean burrow length was 2.7 m ± 1.8 SD (n = 5, range: 1.3–4.9 m) and mean den depth was 0.48 m ± 7.8 SD (n = 5, range: 0.42–0.57 m) below the soil surface. Animals were never found foraging in daylight. Although no animals were found with eggs or young in the pouch, 1 individual was lactating when captured in April 2002 and again in April 2005. The data generated by this study provide valuable insights into echidna biology that will facilitate efforts to conserve populations of these unusual mammals.