Because the objective of a study will largely determine the methods used, it is essential to define the objectives at the outset. Very broadly, studies may be defined as either extensive and intensive. Extensive studies are carried out over larger areas or longer time periods than intensive studies, and are frequently used to provide information on distribution and abundance for conservation or management programmes. Intensive studies involve the repeated observation of the population of an animal. The different types of population estimates—absolute, relative, and intensity—are described. The estimation of error and confidence intervals, including jackknife and bootstrap techniques, is described.