Field experience obtained through photovoltaic test and application experiments sponsored by the US Department of Energy has offered an opportunity for solar cell module reliability assessment and improvement. Through a formal problem/failure reporting and analysis system, field problems have been identified and characterized. The causes of field failures have been analyzed with respect to environmental and operational stresses and to induced degradation mechanisms. On the basis of these results, manufacturers have improved the reliability of later generations of modules through changes in design, material selection, and manufacturing controls. This paper summarizes field experience, describes key failure modes, and evaluates industry progress in addressing such problems.