Angular Differential Imaging (ADI) is a high-contrast imaging technique that reduces quasi-static speckle noise and enhances the detection of nearby companions. The technique involves acquiring a sequence of images with an altitude/azimuth telescope while keeping the instrument field derotator off, allowing the field of view (FOV) to rotate relative to the instrument. A reference PSF is constructed from other images in the sequence and subtracted to remove quasi-static PSF structure. The residual images are then rotated to align the FOV and combined. ADI can reduce quasi-static PSF noise by a factor of approximately 5 per image subtraction, and combining all residuals provides an additional gain proportional to the square root of the total number of images acquired. For one-hour observing sequences, a total speckle noise attenuation of 20-50 is achieved compared to a single 30-second exposure. For two-hour sequences, ADI achieved a 100-fold PSF noise attenuation for Vega, reaching a 5-sigma contrast of 20 magnitudes for separations greater than 8". ADI offers 30 times better signal-to-noise than classical observation techniques over a 30-minute sequence. The technique is suitable for searching for exoplanets with masses similar to Jupiter (1-2 M_J) orbiting young stars at distances between 50 and 300 AU. The paper discusses the performance of ADI using data from the Gemini North telescope and the Altair adaptive optics system, and compares it with classical imaging techniques. The authors also explore the potential of combining ADI with other high-contrast imaging methods.Angular Differential Imaging (ADI) is a high-contrast imaging technique that reduces quasi-static speckle noise and enhances the detection of nearby companions. The technique involves acquiring a sequence of images with an altitude/azimuth telescope while keeping the instrument field derotator off, allowing the field of view (FOV) to rotate relative to the instrument. A reference PSF is constructed from other images in the sequence and subtracted to remove quasi-static PSF structure. The residual images are then rotated to align the FOV and combined. ADI can reduce quasi-static PSF noise by a factor of approximately 5 per image subtraction, and combining all residuals provides an additional gain proportional to the square root of the total number of images acquired. For one-hour observing sequences, a total speckle noise attenuation of 20-50 is achieved compared to a single 30-second exposure. For two-hour sequences, ADI achieved a 100-fold PSF noise attenuation for Vega, reaching a 5-sigma contrast of 20 magnitudes for separations greater than 8". ADI offers 30 times better signal-to-noise than classical observation techniques over a 30-minute sequence. The technique is suitable for searching for exoplanets with masses similar to Jupiter (1-2 M_J) orbiting young stars at distances between 50 and 300 AU. The paper discusses the performance of ADI using data from the Gemini North telescope and the Altair adaptive optics system, and compares it with classical imaging techniques. The authors also explore the potential of combining ADI with other high-contrast imaging methods.