The haematology laboratory is able to perform a number of tests to help establish the cause of illness in children. The full blood count (FBC, also known as a complete blood count, CBC) is one of the most basic blood tests performed on children attending hospital or a primary care clinic. All doctors should therefore have an understanding of how the test is performed, possible pitfalls, be able to interpret results and know when more specialised testing or advice is required. Other haematological investigations in routine use include coagulation screens, blood film examination, reticulocyte counts and methods for estimation of iron stores and detection of abnormal haemoglobins. This chapter will focus on these basic tests and simple algorithms for the subsequent investigation and differential diagnosis of the commonest haematological abnormalities encountered in general paediatric practice.