Chapter 23 was an introduction to macroeconomics: macroeconomics studies the behavior of the economy as a whole. It is primarily concerned with two topics: long-run economic growth and the short-run fluctuations in output and employment that are often referred to as the business cycle. These phenomena are closely related because they happen simultaneously. Economies show a distinct growth trend that leads to higher output and higher standards of living in the long run, but in the short run there is a great deal of variability. Sometimes growth proceeds more rapidly and sometimes it proceeds more slowly. It may even turn negative for a while so that output and living standards actually decline, a situation referred to as a recession. This chapter provides an overview of the data that macroeconomists use to measure the status and growth of an entire economy as well as a preview of the models that they use to help explain both long-run growth and short-run fluctuations.