Ranked set sampling (RSS)is a novel method of achieving observational economy compared to Simple random sampling (SRS. Often we are faced with situations where measurements on the actual variable are costly and time consuming. However, if we can rank the items by mere inspection, according to the variable without taking actual measurements, this often happens in environmental monitoring and assessment that require observational data.In this book we obtain the utility of ranked set sampling over the simple random sampling with the help of numerical illustrations. In the next chapter of the book we have proposed an adaptive cluster sampling theory based on ranked sets.