Screening means application of tests to individuals who are yet to show clinical manifestation of disease. It does not diagnose disease. It differs from early diagnosis which means detecting a disease in symptomatic persons. A disease suitable for screening is one which has one of the following- it’s a serious disease, early diagnosis reduces morbidity, prevalence is high, natural history is known, effective treatment available and treatment should be feasible and acceptable. Screening test should be easy to apply, inexpensive, should not cause any harm and test results should be valid and reliable. Validity of a screening test is tested by- sensitivity, specificity, positive predictive value, negative predictive value. Benefits of screening are- can improve health by detecting disease in preclinical stage, helps in control of disease, detect risk factors, create awareness and useful before disease detection camps. Types are—mass screening and selective or high risk screening. Biases could be- selection bias, incidence—prevalence bias, length bias and lead time bias.