Protecting a threatened species requires a firm grasp of its population biology. Biologists are increasingly relying on innovative methods to track wildlife populations and demographics. Long-term monitoring using biodiversity inventories, population censuses, and demographic studies can reveal temporal changes in population size and distribution and help to distinguish short-term fluctuations from long-term decline. Among the most popular methods, however, are market surveys, hair snares and faecal sampling, while photos taken by tourists and camera traps have also been used to obtain population-level data. Population viability analysis (PVA) uses demographic, genetic, and environmental data to predict changes in population sizes and extinction risk over time. Likewise, sensitivity analysis can be used to guide conservation action by estimating how different management actions will affect a population’s extinction probability. Minimum viable population estimates can be used to determine how many individuals are needed to reduce the threat of extinction, while maximum sustainable harvest estimates can be used to set harvest limits on species threatened by overharvesting. Unfortunately, many surveys are poorly designed, leading to biased data, poor survey precision, and misleading results, which hamper our ability to halt biodiversity losses. To overcome these challenges, surveys should be representative, sufficiently large, and conducted repeatedly over time.