This textbook describes several diseases and clinical conditions, from physiopathological mechanisms to main clinical pictures, highlighting the importance of laboratory medicine, with the aim to provide the necessary tools for guiding correct laboratory findings interpretation. Indeed, it is now widely recognized that laboratory medicine has a pivotal role in clinical medicine, significantly influencing clinical decisions. Thus, it is crucial to understand and use laboratory data appropriately. This book has the great advantage of describing each topic exhaustively in order to facilitate its understanding. Specifically, it describes both diseases with a high incidence in the population, such as Diabetes Mellitus, Cardiovascular Diseases, Dyslipidemias, and Autoimmune Diseases, as well as rare diseases, such as Hereditary Metabolic Diseases. In addition, unusual topics are treated, such as Clinical Biochemistry of the Mind, as well as hot topics, such as Biological Drugs, Biobanks, Health Technology Assessment, and Omics Sciences. Finally, the book includes a chapter on the new health emergency, the SARS-CoV-2 pandemic. Two appendices are provided at the end of the book: a table summarizing the reference range and decisional cut-off for the main laboratory parameters and instructions on performing a venous blood sample. The book will be an invaluable tool for medical and biomedical students, as well as for practitioners.