The ultimate purpose of this book on economic evaluation is to be a text for consultation and inspiration to anyone who wishes to design, carry out and analyse an economic evaluation of a drug or health technology, in order to obtain valid and quality results and thus serve to make better health-related decisions in our country. Unfortunately, the resources available in our National Health System to cover all the healthcare needs of our society are ever more limited; therefore, it is absolutely necessary to prioritise the allocation of resources and to use these resources to finance the therapeutic options that are most efficacious, safe and cost-effective (that will achieve the best health results in patients with the monetary investment carried out). Economic evaluations will be instruments of invaluable help for healthcare professionals and other decision-making agents of the system when it comes to making a more efficient use of existing resources, maximising the therapeutic benefit.