Two main psychopathology-based approaches to detection of the prodrome have emerged; the Ultra High Risk (UHR) and Basic Symptom approaches. Conversion risk varies between studies using these approaches and in one centre conversion rates are reported to be decreasing year on year. There is a need examine the conversion risk across studies to establish a pooled estimate of risk for instruments designed to detect the prodrome of psychosis. To maximise the detection of those thought to present a risk of psychosis the Lancashire Early Assessment and Detection (LEAD) clinic uses an UHR instrument, the Comprehensive Assessment of at Risk Mental States (CAARMS) and A Basic Symptom instrument, the Schizophrenia Proneness Instrument (SPI-A). The thesis had two broad aims 1) to conduct a systematic review with meta-analysis of the research field to date and identify areas for further research, 2) to establish the accuracy of the LEAD clinic predictions. The meta-analysis involved a systematic search of MEDLINE, EMBASE, PsychINFO and CINHAL identifying studies of psychopathology-based instruments for the detection of the psychosis prodrome. The service evaluation examined for conversion to psychosis in patients examined for Basic Symptoms (SPI-A), attenuated positive symptoms (CAARMS), schizotypy (SPQ-A) and social functioning (SOFAS).The meta-analysis found that both the UHR and Basic Symptom approaches yield similar results. The differences in the positive predictive values (PPV) of the two approaches were not significant (Basic Symptoms, 0.34, UHR 0.25). The service evaluation found over a third (n=58) of referrals to the LEAD clinic to be psychotic at baseline and sixty-four patients to have an at risk mental state (ARMS). Conversion risk for CAARMS was 36.67%. and was 28.57% for SPI-A. The COGDIS criterion of SPI-A was found to be the most predictive with a PPV of 0.43, a sensitivity of 0.80. When patients met a combination of both COGDIS and CAARMS the likelihood ratio increased to 5.25 although the sensitivity was low (0.47).Overall, the findings of the thesis indicate that both the Basic Symptom and UHR approaches are valid for use in routine clinical settings for the assessment of psychosis risk. The thesis found that a combination of both approaches could provide future opportunities research. The SPQ-A schizotypy assessment was found to correlate with the attenuated symptom criterion of CAARMS and evidence suggests that the SPQ-A score increases closer to transition. The SPQ-A could offer opportunities for developing efficient methods of monitoring progression of prodromal symptoms.