Testing vocabulary is similar to testing in other areas of language knowledge and use. The same criteria of reliability, validity, practicality, and washback need to be considered when designing and evaluating vocabulary tests. In some ways testing vocabulary is easier than testing grammatical knowledge or control of discourse because the units to test are more obviously separate. It is not too difficult to identify what a word type is. However, there are problems and issues and we look at these in this chapter. This chapter has two major divisions. The first major division looks at the purposes of vocabulary tests, covering diagnostic, placement, achievement, and proficiency tests. The second major division looks at different test formats, answering questions like: Should choices be given? Should words be tested in context? How can I measure words that learners don’t know well? This section covers a wide range of vocabulary test formats, along with comments on their design and use.