Haemaphysalis longicornis is the only tick in New Zealand that infests livestock. Throughout its range H. longicornis is exposed to and exhibits tolerance to a wide range of environmental conditions, although it flourishes more in moist, warm-temperate environments. This review examines aspects of the biology, physiology and ecology of H. longicornis that determine its distribution and seasonal activity in New Zealand, based on laboratory and field studies. Examples are also drawn from studies outside New Zealand for comparative purposes, especially in the context of seasonal activity as seen in less temperate latitudes. The tick is able to withstand a wide range of temperature, from its developmental threshold of ∼12°C to nearly 40°C at its lethal limit, but its tolerance of dehydration is less wide, especially in the larva and adult, the former especially being the stage that largely determines suitable biotopes for the tick and its present distributional limits. The importance of H. longicornis to the New Zealand livestock industry has recently increased through the establishment and spread of Theileria orientalis Ikeda among dairy and beef cattle, although the tick has always posed production-limiting problems for cattle, deer and to a lesser extent, sheep. The tick's role as a vector of theileriosis and how aspects of the tick's biology affect the spread and maintenance of this disease are discussed. It is proposed that, of available wildlife hosts, the brown hare with its wide-ranging habits, is an important disseminator of ticks. Currently control of ticks is difficult partly because of their wide host range, overlapping activity periods of stadia, and also because the greater part of their annual cycle is spent on pasture. This means that acaricides alone do not satisfactorily reduce tick populations or provide comprehensive protection to stock, so integrated management combining pasture management with good husbandry and chemical prophylaxis is advocated.