Microbiological and histopathological assessments are core investigative procedures when trying to achieve a diagnosis. Despite being ‘behind the scenes’ and not in direct patient-facing roles, microbiologists and pathologists have a great responsibility in carefully reviewing processed patient specimens. At times, a diagnosis may be achievable from a standard smear, culture or haematoxylin and eosin-stained slide. However, in other situations, the diagnosis may not be so straight forward and other special tests will need to be employed for a diagnosis to be achieved. In this chapter, we will explore the range of tests available, review the supplementary additional tests that may be required in special situations and learn how microbiologists and pathologists work within a multi-disciplinary team environment to ensure patients receive the correct treatment for their presenting disease process.