Consumers of psychological tests have a large number of tests to choose from these days and often have little factual information that can be used to pick a particular test. Googling tests for hiring employees results in roughly 48,200,000 hits, personality tests has 10,300,000 hits, integrity tests 7,220,000 hits, and tests to hire salespeople 693,000 hits. Clicking on some of these sites, we found claims such as “Never hire a bad salesperson again”; “Our sales assessment validity is backed by brain research. No other sales assessment is”; and “You can start testing your job candidates today—it’s that quick and easy!” These quick-and-easy fool-proof solutions might seem attractive to employers who need a hiring solution but have little expertise to choose among tests and vendors. Fortunately, industrial-organizational psychologists have conducted more than 100 years of research and practice that can help people choose tests appropriate for a particular job. In this chapter, we review some of the key concepts underlying the science of testing, particularly reliability and validity. Then we discuss how employers can use these concepts, as well as relevant information that should be provided by any reputable test developer (but which often is not!) to choose a particular test best suited for particular needs.