The process of identifying the illness with the aid of symptoms and indicators is known as medical diagnosis. A correct diagnosis is necessary for prognosis, treatment, proper control measures, epidemiology, and the history of the disease. It is instrumental to identify disease at an earlier stage before symptoms are distinct. Many types of disease diagnoses can be detected. Endoscopy, laparoscopy, colposcopy, and histological examination-ray imaging are some of the widely used diagnostic tools. Certain tissues, such as the urinary system in urography and the arteries and veins in angiography, can be imaged using X-rays in conjunction with specific contrast agents. Information about the function of the heart can be obtained by electrocardiography. Ultrasonography is most frequently used to assess fetuses in utero. The detection of a fetal heartbeat, the mother's sense of fetal movement, and an ultrasound proving pregnancy were detected by sonography. Radioimmunoassay (RIA) is used to measure human chorionic gonadotropin. Machine learning techniques may give medical professionals new resources for illness screening, detection, and diagnosis. The chapter concludes with various diagnostic techniques and it draws attention to the availability of diagnostic testing to receive the right care to save lives by improving the prognosis of diseases.