Research in medicine is liable to all rules and standards that apply to research in other natural sciences, since medicine as a science and service fully meets the general definition of science: it is a common, integrated, organized and systematized knowledge of mankind, whereby physician--being more or less aware of doing so-- in his daily activities applies scientific thinking and scientific methods. The procedure of problem solving in scientific work and in medical practice is characterized by many similarities as well as variation. In scientific research, the observation of some phenomenon that cannot be explained by the known facts and theories is followed by making a hypothesis, planning and carrying out experimental investigation resulting in some data. Interpretation of these data then provides evidence to confirm or reject the hypothesis. In medical practice, quite a similar procedure is followed; the initial examination of a patient, when his condition cannot be explained by the data thus obtained, is identical to the observation of a phenomenon which cannot be explained by the known facts; working diagnosis would correspond to making the hypothesis; and experimental investigation would compare to laboratory and other diagnostic studies. The working diagnosis is accepted or rejected depending on these results. Of course, there also are differences in the problem solving procedure between scientific research and daily medical practice. For example, in research a single hypothesis is posed, a single experiment with successive testing and/or repeats is performed, whereas in medical practice several hypotheses are made, multiple studies are concurrently performed to reject current hypotheses and to make new ones. Scientific investigation produces an abundance of systematic data, whereas in medical practice target data are being generated, yet not systematically. Definitive decision making also differs greatly, as in scientific research it only ensues from conclusive evidence, whereas in medical practice definitive decision is made and therapeutic procedures are performed even before reaching final evidence. The general strategy of work and research in medicine can be briefly described by four principles, i.e. good knowledge of one's own work; continuing upgrading of one's own work in collaboration with respective institutions (laboratories, university, and research institutes); implementation of standard, up-to-date and scientific methods most of the time; and publishing work results on a regular basis. This strategy ensures constant progress and treatment quality improvement while allowing due validation and evaluation of the work by the society. Scientific research is based on the pre-existing knowledge of the problem under study, and should be supervised, systematic and planned. Research produces data that may represent some new concepts, or such concepts are developed by further data processing. In research, scientific procedure includes a number of steps that have to be made to reach a new scientific result. This procedure includes (a) thinking about a scientific issue; (b) making a scientific hypothesis, i.e. the main objective of the study; (c) research ethics; (d) determination of sources and mode of data collection; (e) research performance; (f) collection and analysis of all research data; (g) interpretation of results and evidence; and (h) publications. The next section of this chapter brings an example of scientific research in the field of medicine, where the procedures carried out during the research are briefly described; other chapters of this supplement deal with statistical methodology used on processing the data obtained in the study, which is most frequently employed in scientific work in the field of medicine.