Scientists use sampling to get an estimate of things they cannot easily count. A population is made up of all the organisms of one species living together in one place at the same time. All of the people living together in one town are considered a population. All of the grasshoppers living in a field are a population. Scientists keep track of the change (increase or decrease) of population numbers to make decisions about issues that affect that population. For example, marine biologists count the number of different fish species to see what effect fishing might be having on them. Fishery managers use this data to determine how many fish can be caught without damaging a population. It is often not practical or even possible to count all the members of a population. A population can be so large that counting it would be like trying to count the number of grains of sand on a beach. Animals can be difficult to count because they live underwater, move around a lot, or are only active at night. To get around these counting problems, scientists take data from just a small portion of the population called a sample. They take several samples and then use the average size of those samples to calculate an estimate of the entire population size. This article briefly discusses how sampling works through an activity on sampling grasshoppers.