This memo should be an overview of sampling, starting with the definition of what sampling is, when and how it is used, leading to a discussion of the different types of sampling and the risks associated with them . The memo will also discuss the steps involved in sampling and the role of sampling in the audit, including attribute sampling and variable sampling. Sampling involves drawing an efficient conclusion about a population of interest by testing the gained assurance on a subset of that population, which is called a sample, at a lower cost in time and money than testing the entire population. However, the trade-off between efficiency and effectiveness always exists. In other words, sampling would be used when the efficiency gains outweigh the effectiveness loss. Since sampling only tests a small group of samples in the population, which can cause loss of effectiveness, sampling risk always exists. Sampling risk is defined as the probability that there will be a difference between the conclusion drawn from testing the sample and that from testing the entire population. For example, one company offers a snack with three flavors, A, B, and C, all aimed at the teen market. The company carried out sampling to decide which product to focus on most. By giving 10 points to each participant and asking them to assign points to the three flavors after trying, the researchers will calculate the total credits earned from each flavor. The conclusion of the test on 100 participants from the population shows that A got more credits, however, the real The result is that C is the best-seller. The difference is called sampling error and occurs when a sample is an unrepresentative group of the population. Therefore, to control sampling, the population consists of all components or transactions in the account balance or transaction class. Auditors use sampling to increase efficiency while maintaining the appropriate level of effectiveness, however sampling risks can cause different and unexpected results. From the form we can see how closely the results are related to each method and steps used in sampling, and this is why auditors should know how to sample and what to do to control risks. In conclusion, this memo has provided good guidance and explanation on what sampling is, when and how auditing is used both regularly and in the auditing aspect. It also indicated the risks involved in sampling and the methods for controlling these risks. The specific plans used in this process and how auditors use them in auditing a client are detailed step by step.