The receiver operating characteristic (ROC) curve is a standard method for quantifying the performance of a detection task where the signal of interest is embedded in noise. ROC analysis has been applied to a variety of signal detection problems including medical imaging, acoustics, and automated target detection (ATD). The free response operating characteristic (FROC) curve generalizes the ROC model for search problems. The FROC model is appropriate when multiple detections are possible and the number of false alarms is unconstrained. The shape of the FROC curve depends on the underlying probability distributions for the signal and noise. The general FROC model is presented and parameter estimation is discussed. An example illustrates the approach.