The Te Maari Craters on the northern side of the Tongariro Cone Complex represent one of at least seven vent systems that have been active on Tongariro since the last glacial maximum. Activity at Te Maari had begun by at least 14 ka and has continued through historic times, making it one of the most long-lived of the young eruptives on Tongariro. The older lower crater is a wide (500 m), inclined, flat-floored structure up to 60 m deep, which exposes multiple layers of jointed andesite lava. The morphology of this structure implies some shallow collapse probably associated with withdrawal of a shallow magma chamber. The upper crater is a steep-sided, funnel-shaped feature constructed from weakly consolidated, very coarse, monolithic andesite breccia, and is largely the product of explosive eruptions through a pre-existing fan of thick, very coarse auto·breccia. The most recent lava flow (probably around 1500 AD) and explosive ash eruptions (notably in 1892 and 1896) have been sourced from this upper crater. There are 4 older northern lava flows sourced from vents in the vicinity of the craters. From historic observations and analysis of the erupted products in the field, the typical eruptive style of these craters range from phreatic - phreatomagmatic to vulcanian. There is no evidence for more explosive subplinian eruptions from the Te Maari crater system. The explosive eruption of 1896 was of sufficient intensity to disperse ash at least as far as the Hawkes Bay, and up to 50 mm of ash accumulated on the Desert Road. A repeat of this eruption today would cause severe disruption to agriculture and forestry operations, as well as critical transport and utility networks in the central North Island. The Tongariro Power Scheme would also be affected, as ash fall over Lake Rotoaira would cause damage to hydroelectric power facilities. A lava flow from these craters today on the scale of the 1500 AD flow would also have a major impact on transport networks if it reaches the State Highway, and outgassing would cause local acid rain and health problems in nearby communities such as Turangi and Taumarunui. The location of these craters close to the boundary of the national park also presents a unique hazard, as it would be difficult to prevent members of the public from gaining access to the area following an eruption and endangering their lives through curiosity. Recent seismicity beneath the craters is a reminder that further eruptions are likely from the Te Maari system. Work on these craters to characterise the mechanisms, timing and magnitudes of typical eruptive activity contributes valuable information in the assessment of the probability and impacts of future eruptions.