This review outlines some of the difficulties involved in assessing preschool children's language development. Language is a sensitive indicator of a range of developmental difficulties yet the accurate identification of children who are experiencing delays or disorders is problematic. A range of different approaches are used to identify and assess language problems including norm-referenced assessments, questionnaires and language samples. Each of these is critically evaluated. In particular the reliability and validity of the measures and their ability to discriminate atypical patterns of development is considered. It is concluded that there are no simple assessment tools that identify and assess language development. Moreover, the use of single measures is considered inadequate for determining whether a child at any age has typical or delayed language. Ways to circumvent the limitations of the assessment tools are considered.