The duty to administer clinical care to a diverse population that is connected solely by the severity of their illness is what makes medicine special. Nowadays, we have access to hundreds of different diagnostic techniques. Choosing the right diagnostic test for a particular clinical circumstance is one of the challenges that professionals in the medical field regularly confront. It is best to utilize a test that is accessible, reliable, repeatable, and appropriate for the circumstances at hand whenever possible. This little book aims to provide a simplified approach for choosing and interpreting investigations. Since providing a strong clinical viewpoint was our main objective, all of the contributors are practising physicians. We would greatly appreciate any comments from readers, as there may have been tests that we missed, there may be typos in the text, and there are a number of other changes that we may, and will, make in subsequent editions.