A new sensor for evaluating fruit and vegetable firmness is presented while exemplifying application by reporting some results on measuring firmness of tomatoes. The firmness sensor comprises a small electrodynamic vibrator, which contacts the fruit and applies a series of minute input oscillations of a predetermined frequency and amplitude profile, optimized for each particular fruit type. These input oscillations are monitored by an acceleration transducer attached to the vibrator head. The output oscillations on the other side of the fruit, are measured by a similar transducer attached to the sensor finger, which gently contacts the fruit by a controlled force. The signals from the transducers are acquired by a microcomputer, which computes a firmness index, based on the difference between the output and input oscillation profiles. Firmer fruits transmit a larger portion of the input signal than softer fruits. For quality control and shelf-life prediction, the firmness of tomato samples may be measured manually, by a bench-top version of the apparatus. For research and for optimal harvest time determination, the portable hand-held version of the apparatus may be used for monitoring the firmness of tomatoes as they grow in the field or greenhouse.