This is the second part of a series on case reports and case series studies. It will help junior researchers to comprehend what is the case series/exposure series as a type of research. It highlights the definition, types, importance, limitations, and differences between case series and exposure series. Examples of important historical case series that were instrumental in the early identification of health problems will be mentioned. A special editorial will be devoted to consecutive controlled case series (CCCS)/ self-controlled case series (SCCS) as an important research method.