Sentence completion tests are a class of semi-structured projective techniques. Sentence completion tests typically provide respondents with beginnings of sentences, referred to as “stems,” and respondents then complete the sentences in ways that are meaningful to them. The responses are believed to provide indications of attitudes, beliefs, motivations, or other mental states. There is debate over whether or not sentence completion tests elicit responses from conscious thought rather than unconscious states. This debate would affect whether sentence completion tests can be strictly categorized as projective tests.

A sentence completion test form may be relatively short, such as those used to assess responses to advertisements, or much longer, such as those used to assess personality. A long sentence completion test is the Forer Sentence Completion Test, which has 100 stems. The tests are usually administered in booklet form where respondents complete the stems by writing words on paper.

The structures of sentence completion tests vary according to the length and relative generality and wording of the sentence stems. Structured tests have longer stems that lead respondents to more specific types of responses; less structured tests provide shorter stems, which produce a wider variety of responses.