This document discusses different types of sampling plans used for quality control including single sampling, double sampling, multiple sampling, and sequential sampling. Single sampling uses one sample to make an acceptance or rejection decision while double sampling allows for a second sample if the first is on the borderline. Multiple sampling may require more than two samples with smaller sample sizes at each stage. Sequential sampling selects units one at a time and makes decisions after each unit until acceptance or rejection occurs. The document provides examples and compares the advantages and complexities of each approach.