This work presents several major developments related to a fluorescence confocal microendoscope technology that can provide instantaneous cellular level images from selected depths of tissue inside the human body. The confocal microendoscope systems discussed employ fiber-optic based imaging catheters coupled to custom built slit-scan confocal microscopes. One major new development involves the design, development, and testing of a new flexible confocal microgastroscope (CMG) system for imaging the esophagus. This new system has the potential to aid in the early detection of esophageal cancer. It consists of a new optical scan unit mounted on an endoscopy cart and a new flexible catheter that can be inserted through the instrument channel of a commercial gastroscope. The CMG system has higher spatial resolution and larger field of view than the previous generation clinical confocal microendoscopes in our lab. In addition, the new CMG system can be operated over a greater wavelength range than its predecessor. Central to the CMG system is the design, construction, and testing of a new distal miniature objective that enables high-quality microendoscopy. The miniature objective, built with all glass spherical surfaces, achieves diffraction-limited performance over a 486 to 1000 nm spectral range. The wide achromatic range of this lens allows the CMG system to be used with a variety of contrast agents including agents in the NIR region. In addition, the new miniature objective can be mounted on existing confocal microendoscopes in our lab such as the ovarian clinical confocal microlaparoscope and our laboratory based experimental system. Finally, a new confocal microlaparoscope with an articulating catheter capable of imaging inside the distal portion of fallopian tubes is presented. This instrument is intended to allow the detection of early stage ovarian cancer originating inside the fallopian tube. The new microlaparoscope is compatible with 5 mm trocars and includes a thin 2.2 mm diameter articulating distal tip consisting of a bare fiber bundle and an automated dye delivery system. The distal tip of this new endoscope can be articulated through simple wrist movements and locked in place at a given angle if desired. The thin distal tip and the ability to control the angle of the tip provide the size and flexibility needed to image inside the curved and delicate structures of the fallopian tube. Preliminary imaging results from the new CMG system, the achromatized miniature objective, and the new articulating confocal microlaparoscope are presented to demonstrate the performance and the potential of each system towards the overall goal of in vivo imaging and disease diagnosis.