Most neuropsychological examinations are performed with the ultimate goal to improve the patient's quality of live. Hence, patients have everything to gain from giving their best effort. However, wittingly or unwittingly, some patients may give distorted of erroneous responses that are not in correspondence with their actual neuropsychological status. It is important to identify such non neurological contributions. This chapter focuses of methods to determine whether aspects of the neuropsychological performance have been distorted by poor effort or response bias for whatever reason, or by outright malingering. Traditionally, four sources are used for this manner: (1) evidence of consistency in the history of examination; (2) the likelihood that the set of symptoms and the neuropsychological test profile make medical sense; (3) an understanding of the patient's present situation, personal and social history, and emotional predispositions; (4) emotional reactions to their symptoms and complaints. Although a large-scale meta-analysis (1996) concluded that neuropsychologist's judgement in general is reliable and moderately valid, the effectiveness of traditional strategies has been sharply questioned. Nowadays, it is becoming increasingly common for neuropsychologists to include in their assessment batteries some tests that are developed to assess effort, symptom validity, and malingering. A yet unresolved issue is whether patients should be warned that the test battery will include measures of effort and response bias. Finally, an important note on using such tests: findings of measures designed to assess performance validity and response bias should not be interpreted outside the context of clinical history and other measures of cognitive function.